The 50 million dollar lie - <AUTHOR> http://garyrubinstein.teachforus.org/2013/01/09/the-50-million-dollar-lie/ <comment><USER2> I know nothing about the domain of teacher measurement, and have no opinion on it.

But the first chart in the blog post, with the big mass of blue on it, is surely not the strong evidence of weak correlation, that the author is making it out to be?

There could still be a strong correlation in that data, even if it looks like a blob of blue - because there are so many data points on that chart, that we can no longer tell where the density of points is. Its possible that there is a dense line of points in there that still gives a strong correlation, that we just can't see.

A heatmap with some level of binning, or a hex bin chart, or 2d histogram, would surely be more appropriate in these circumstances? Something like this: [http://matplotlib.org/examples/pylab_examples/hexbin_demo.ht...](http://matplotlib.org/examples/pylab_examples/hexbin_demo.html)

Maybe along with some direct math analysis of the correlation. Am I missing something?

<comment><USER3> A heatmap would be more revealing, but I'd eat my hat if it weren't a standard distribution (and I had a hat). It's nature (but hey, anything's possible). The scales are only slightly skewed, but we're not talking logarithms. The merit of the scales ("value-added") on the other hand, is very questionable.

But the relation, whatever it is describing, is pretty weak since the ellipse isn't very irregular (it's only "slightly" irregular). [http://www.emeraldinsight.com/content_images/fig/08702801090...](http://www.emeraldinsight.com/content_images/fig/0870280109015.png) Think Kepler's laws.

Edit: The first post in the series shows a scatter of the direct (non-delta) scores, and it looks like San Fransisco in the morning: [http://garyrubinstein.teachforus.org/2012/02/26/analyzing- re...](http://garyrubinstein.teachforus.org/2012/02/26/analyzing-released-nyc- value-added-data-part-1/)

<comment><USER4> Sorry don't mean to belabor this point but I think "standard distribution" (changed from standard deviation) is still incorrect. "Standard" referers to standardized parameters (i.e. mean, variance) as in "standard normal" which has a mean of zero and variance of one (and standard deviation of one). Certainly not the case here. Maybe you mean "bivariate normal with positive correlation"?

[http://en.wikipedia.org/wiki/Multivariate_normal_distributio...](http://en.wikipedia.org/wiki/Multivariate_normal_distribution)

Interesting thing is the (positive) means and variance seem similar which is consistent with underlying random variable being the same.

<comment><USER3> Yes, you are right. I wasn't being especially rigorous, and technically correct is the "best kind" of correct. :)

<comment><USER4> No worries. Statistics can be very confusing. Part of the reason it is so confusing is all the sloppy usage we come across in the media and on the internet.

Everyone wants to use statistics as a tool to bolster their point of view but don't want to bother to actually learn enough statistics to deal with the situation they are trying to analyze.

</comment></comment></comment></comment></comment><comment><USER5> This is a surprising blog post in that I draw the complete opposite conclusion the author does. The author seems to think that the averaging hides volatility (which it does), which leads to incorrect conclusions drawn. Whereas to me it looks like it removes visual noise to show an actual trend.

In his original scatter plot, because of the big ball in the middle it's easy to handwave and say, "look a random blob" -- but even a slightly longer look seems to indicate there is a positive correlation in the data. His averaging that he does at the end, IMO, makes it clear.

<comment><USER6> The other thing the author does is to derive absolute findings when the author himself admits to making an assumption about how the numbers were obtained. To me, using the word "lie" in the title is therefore nothing more than click- baiting.

And on a separate note - there's a lot of anti-Gates sentiment flying around lately. Whether his methods are the best or not, he's _using his own money_. I find it really difficult to give any criticism directed at Bill Gates' foundation any credence. And that not knowing much at all about what he does.

Maybe people would like Bill more if he did a Larry Ellison and bought a yacht instead.

<comment><USER7> People are arguing that he is using his own money to actively damage society. I'm not sure if I agree with that, but to say you can't criticize someone for what they do with their money is ridiculous - as an extreme, he could use his money to poison people, or to lobby for life sentences for marijuana use.

<comment><USER6> I said Bill Gates, and not someone. And while I don't know how people think he's damaging society, if the article being discussed here is representative then I remain unconvinced. This is not an invitation to enlighten me. I'm not wasting my time reading yet another opinion, assumption or half-baked arm- chair allegation. The investment dollars and opinion of the likes of Warren Buffett are a much more compelling endorsement to me than (I mean this respectfully) members of HN.

</comment></comment></comment></comment><comment><AUTHOR> I suspect there'll be a lot of differing opinions on this, and I'm looking forward to seeing the discussion. What would be helpful would be if people could say how much experience they have in hard statistics, and how much what they say is driven _a priori_ from the data.

I know that hackers, in particular, have real problems with "Argument from Authority", but stats is one place where it's really, really easy to go wrong, so knowing how much formal training someone has can be an important indicator.

<comment><USER8> I'll bite. I won't discuss my experience in my posts since I don't want to argue from authority but will do so below. But first, I should point out that you're committing a similar sin to that which is alleged in the article. What you really care about is the correctness of an argument. You hypothesize that formal training is an important indicator of correctness. Presumably there's also noise in that scatterplot but we don't even have it. Since it's the best thing available, you are choosing to rely on it.

As for my formal stats training: None beyond High School. That said, I've worked with and interviewed many with far more training. One thing, I learned is that most people don't have great intuition for statistical problems and it's not terribly highly correlated with years of schooling. I've met PhD's in economics and statistics who have made basic conceptual errors as well as those with less training who were more reliable.

So while training may be correlated with accuracy, you should still demand a well-reasoned argument and think critically about it.

<comment><AUTHOR> I agree almost entirely. I'm specifically not asking for people to say "I'm a PhD in statistics, and here's the answer. Accept it because I know better than you." What I'm asking for a a complete and reasoned response, along with some evidence as to how much I should listen to you in the first place.

If you have no such evidence then the onus will be on you to make your argument more complete, more coherent, and more comprehensive. If you have evidence (note: evidence, not proof) then you can be a little less rigorous in what you say, and rely on people giving you the benefit of the doubt while they work through the argument.

What I see a lot of is long, apparently good arguments, that then turn out not to be as complete or coherent. they sometimes just don't hang together.

Significant amounts of formal study in a subject is evidence that someone might just have a better understanding. After spending a lot of time on the internet I'm tired of having to wade through every single argument in detail looking for all the possible chinks.

Maybe that's just impossible. Maybe every person has to redo every analysis for every argument. Seems like a complete waste of almost everyone's time. What about "Don't Repeat Yourself" or "Don't re-invent the wheel." I guess we are doomed to reinvent the wheel in every single discussion.

<comment><USER8> Reinventing the wheel would be a major problem if our goal is to solve the education problem with this discussion. No one here has done even the basic work I would expect of someone trying to understand teacher evaluation as a solution and compare it to other alternatives.

I would argue that the whole point of HN is to think through arguments in other domains and build intuition by reasoning through problems and arguments. Otherwise, what's the point? No one is going to arrive at this thread and scan the top-rated comments for the solution to his school district's problems.

In cases where actual decisions are being made where the analyses are much more thorough and fully validating much more expensive, other techniques are available. First, one generally builds an awareness of the strengths of each team member which suggests where errors may be more likely. Additionally, one can check a random set of the most likely problem areas. Perhaps, most importantly, while everyone won't re-do every analysis, it's highly unlikely that an any important analysis will only be done once. So one can expect that the high-level results are generally consistent.

</comment></comment></comment></comment><comment><USER9> This blog post linked to from the comments in the article explains the "ecological correlation fallacy"[1] being described in the article:

[http://ed2worlds.blogspot.com/2013/01/gates-foundation- waste...](http://ed2worlds.blogspot.com/2013/01/gates-foundation-wastes-more- money.html)

Key quote:

"...it has been known for more than 60 years now that correlating averages of groups grossly overstates the strength of the relationship between two variables"

Apparently, this was also used in the past to show high correlation between African-Americans and illiteracy.

[1] <http://en.wikipedia.org/wiki/Ecological_fallacy>

</comment><comment><USER10> There are two problems with this article. First is that the "evidence" is from a scatter plot graph, with no statistical measurements attached to it. Stats really aren't something that you can rely on your eyes on. To me, it looks like a weak, positive correlation between previous year's score and current years score. The thing to look for is greater densities in the NE and SW quadrants than the NW and SE. Having a zero-mean "blob" in the data makes it tricky on the eye, but NE and SW points are the ones the model "correctly" predicts, while the NW and SE plots are the ones the models "gets wrong". I think the issue is the eye is looking for a line to process a slope of, but such data doesn't streach into a line. What it should look for is: "given a good score last year, is a good score given this year" or "given a bad score last year, is a bad score given again".

The second issue is that the author does not offer a better solution to the problem. Some information is almost always better than no informantion in decision making. Statistics in human-based samples are always tricky, and its tough to get strong correlations easily. As an aside, this is part of why clinical trials are so tricky and expensive.

(I am not a stats professional, but am a biomedical research scientist with some training in human-population based stats).

<comment><USER11> Exactly. Charts are useful for eyeballing, but only the use of proper statistical tools is valid for showing trends. Charts can easily be very misleading.

There seem to be a lot of comments about the charts on this page. Arguably basic statistics should be a part of every education - is that happening in the USA?

<comment><USER10> Can't comment on USA - in Canada we had an intro in high school then about a 1/2 course-credit module per year from second year until grad school in the engineering programs.

</comment></comment></comment><comment><USER12> " _In New York City, the value-added score is actually not based on comparing the scores of a group of students from one year to the next, but on comparing the 'predicted' scores of a group of students to what those students actually get. The formula to generate this prediction is quite complicated, but the main piece of data it uses is the actual scores that the group of students got in the previous year._ "

[http://garyrubinstein.teachforus.org/2012/03/06/analyzing- re...](http://garyrubinstein.teachforus.org/2012/03/06/analyzing-released-nyc- value-added-data-part-iii/)

Some _qualitative_ comments (from the UK)

An experienced and resourceful teacher may be allocated more 'problem' students than a relatively new teacher as a matter of policy. Teaching students at the extremes of the ability range is harder than the median as the reasons for (say) severe under achievement can be very diverse (learning difficulties, home situation, undiagnosed medical issues - diabetes in my recent experience with one student - and so on) and each student may need a different approach.

I have taught in a few settings over the years. The best teaching happens in my experience in settings where people work together. Performance related pay based on dodgy statistics in an atmosphere of public ridicule does not seem the best way to encourage sharing of practice and teamwork!

"Good luck with that" as I believe the late Mr Jobbs used to say to competitors.

<comment><USER4> You are correct that if students were assigned in some biased manner it could invalidate any relationship between teacher quality and subsequent student performance.

That is exactly what makes this study interesting. All the students were assigned randomly! Much like in a randomized medical study this allows the establishment of a causal relationship.

<comment><USER12> " _All the students were assigned randomly! Much like in a randomized medical study this allows the establishment of a causal relationship._ "

Two thoughts...

1) Ethics: You put some children with dyslexia or with challenging behaviour with newly trained teachers with little experience? Did their parents have any say in this? Was there an ethics process? Was there support available for newly trained teachers meeting major needs in their randomly allocated classes? Amazing.

2) Correlation does not imply a causal relationship. You need a theory. Theory in this area is not positivist, it is fuzzier.

As I said before, 'good luck with that'.

<comment><USER4> 1) Same students, same teachers and same support in same schools but the assignment of students and teachers to classes was randomized. Consent was obtained from principals, teachers and parents.

2) Randomized experiments can establish causation if done properly. This is how medical treatments are evaluated. The theory is simple: teachers that were more effective in the past will be more effective in the future and using objective metrics (tests, classroom observation and surveys) we can measure teacher effectiveness. This certainly positivist but more important likely repeatable.

You seem like you are interested in this but I get the sense you already have strong views. Maybe you should put those aside for a moment and take a closer look at this new and interesting study you might learn something:

<http://www.metproject.org/reports.php>

<comment><USER12> "You seem like you are interested in this but I get the sense you already have strong views."

I will read the reference, however, to those of us in Europe, please remember that this methodology resembles a group of earnest steam punks analysing flies in amber with brass and ebony microscopes on an ice floe that is breaking up... I'm suggesting that we suspect positivist descriptions do not capture the important values in education. 90% of what children learn is learned outside school I suggest.

I am prepared to be astounded with contrary evidence.

</comment></comment></comment></comment></comment><comment><USER13> I'm surprised at the comments here. Seems that nearly everyone disagrees with the blog? Is Bill Gates such a saint among the HN crowd that we ignore statistics for him?

Also, see this blog for some more discussion along the same lines: [http://ed2worlds.blogspot.com/2013/01/gates-foundation- waste...](http://ed2worlds.blogspot.com/2013/01/gates-foundation-wastes-more- money.html)

Seems pretty clear that Gates' study presents the data in a very misleading manner to make a very weak correlation look like a very strong correlation.

<comment><USER14> The blog post doesn't have any statistics to ignore.

Graphs are not statistics. Why doesn't he give us a correlation coefficient on his big blue blob graph?

<comment><USER13> You criticize a short blog post for something that is not done in the Gates publication. Do you have some bias, perhaps? Why does Gates not even give us a scatter plot, let alone a correlation coefficient? This is the critical point raised by the blog.

<comment><USER4> There are quite a few statistics reported in the Gates Foundation publication. Take a look for yourself:

[http://www.metproject.org/downloads/MET_Validating_Using_Ran...](http://www.metproject.org/downloads/MET_Validating_Using_Random_Assignment_Research_Paper.pdf)

<comment><USER13> I never said they don't report "quite a few statistics". I said they don't report this one specific particularly important statistic, and instead obscure it behind a ridiculous averaging procedure. This was either done because they are incompetent or because they are purposely trying to mislead. That's the whole point of TFA.

<comment><USER4> What one particular statistic do you want?

Take a look at the FULL report. All the statistics behind the graph you criticize are in Table 1 on page 10.

The next 40 pages seem to be a pretty competent description of both the strengths and weaknesses of their study.

</comment></comment></comment></comment></comment></comment><comment><USER15> Using LOC to hire or fire programmers ignores important contextual factors, just as using test scores of students to hire or fire teachers ignores important contextual factors. What language is being used? How large is the project? Existing code? Platform? Bug count? Does the person contribute to the team in other ways?

In teacher evaluation you also have critically important contextual factors. What course is being taught? Are the students motivated? What's the classroom like? A lot of ELL kids in the class; does the teacher speak their language?

Many people see _some amount_ of value in these imperfect metrics because they a) seek to measure the critical output (programmers are paid to make code and teachers are paid to make kids learn), and b) simple numeric metrics aren't biased by human fallibility. Popularity amongst peers won't have any impact on LOC or student test scores.

The author feels they shouldn't be used as 33% of the overall evaluation, which is the suggestion made by Gates.

In terms the specific points the author made about Gates' evidence in favor of their suggestion of 33%, I think he's basically right. I haven't read the original study and so I'm assuming for sake of discussion that he's conveying it correctly.

Over saturated scatterplots are not very useful, and in the hands of someone with no training or knowledge of basic statistics they may be dangerous, but they're not wrong. A trained consumer of research, seeing a plot like the author's first, will only be able to conclude that the correlation is not perfect. That rules out only a subset, and a subset that's fairly uncommon outside of the physical sciences, of the possible relationships between two variables. Not very useful, but not misleading unless there's an assumption that the number of data points is relatively small (which may be the case in some research contexts).

Averaging points and then taking the fake aggregated points and plotting those is wrong. It's using a tool to show variability in the wrong way. Averaging hides the variability that is supposed to be shown in a scatterplot. Why not average down to 2 points and draw the line then? Because that's wrong.

I'm thankful that one or two other people here understand, but a bit dismayed at the kneejerk groupthink.

</comment><comment><USER16> I see the OP's point, that visual noise can be filtered in such a way as to create a more compelling trend, and perhaps the filtering that Gates has done has simplified the results...so, OK. Let's not look at charts, let's look at actual calculations that have the various factors accounted for...what are they?

And I guess I'll throw in my two cents into the inevitable teachers-vs-data debate. I believe teachers may be too quick to toss aside performance analysis because they are so close to the personal stories and circumstances...no line chart can seem to account for the student who was improving greatly but then missed an insurmountable number of classtime due to problems at home.

Most humans are unwilling/unable to see their lives and work measured as averages and trend lines and deterministic outcomes, and I think teachers are acutely of this belief due to the nature of their work. And unfortunately, this blinds them to the possibility that while there is no cookie-cutter solution that _always_ works, there are surely some measures/guidelines that _often_ work, or at least mitigate even the most extreme circumstances. As it is, there's not much incentive or opportunity to see "the bigger picture" outside of what happens in one's own classroom year after year.

That said, this is not even close to being mainly the fault of the teachers. Among the other problems is that administrators are just as prone to shortsightedness, and "the numbers" can be wielded by a petty/mediocre principal/district officer to apply pressure to a teacher. It's no wonder that teachers are quick to distrust analyses, given the possibility that they're abused for political means.

So, essentially, it's a giant crapfest with no easy solutions. From the perspective of Gates' efforts, we can only hope that he pours in so much money and advocacy that there's eventually a shift towards best practices...though it's safe to say there will still be unintended consequences that aren't all favorable.

<comment><USER17> _Among the other problems is that administrators are just as prone to shortsightedness, and "the numbers" can be wielded by a petty/mediocre principal/district officer to apply pressure to a teacher._

The more we rely on objective numbers, the less a good teacher has to fear from a bad principal. The principal has no ability to make the teacher's students do worse than their statistical predictor, after all.

On the other hand, many other popular metrics (e.g. principal's opinion/coworker's opinion) can easily be tweaked by a principal who wants to put pressure on a teacher.

</comment></comment><comment><USER8> Both sides are right but they seem to be concerned with different things.

Grouping data points does mask volatility. This doesn't make the effect any less real on the societal level. If we seek to improve student performance, skewing the pool of teachers towards the better ones will do that.

Yet there is also an enormous amount of volatility which is also real. Ideally we would just create better predictors. Constraining ourself for the moment to this set, since they have high error rates on the individual level, it's also reasonable to assert that in relying on this metric, we will make unfair decisions for many teachers.

The right solution depends on how much you value optimizing student outcomes vs. optimizing fairness as well as second order effects such as driving away teachers. My bias would be to use these scores for economic incentives to attempt to ensure that retention for the best teachers is higher than for the worst. Without additional work, termination likely isn't warranted based on this data.

To those who argue that pay differentials require better evidence, I would suggest comparing the validity of performance evaluations across any other job. It's imperfect but better for society than doing nothing.

For long-term fairness, it's important that there isn't a single value-added model. Competitive pressure can do wonders to improve model quality and it's also fairer since those who don't do well on one model can move to a different rubric.

</comment><comment><USER18> He doesn't actually say what the positive correlation is, which I find disingenuous and suspicious. Because his scatterplot is so non-detailed, it's about as useful as the following scatterplot of SAT scores:

X|X

\---

X|X

Where the axes are scores above and below 600 in math on the first and the second time taking the test. There are some individuals who do better or worse - but just because we can draw a detail-obfuscating graph of data doesn't mean there is no detail in the data, or no correlation, or that SAT scores won't help us predict future SAT scores. It just means we can draw a detail- obfuscating graph, and that there's not a perfect correlation.

One point the author does have is that these scores are not perfectly predictive, so bad performance one year shouldn't mean that the teacher gets i.e. fired. OK. He seems to be protesting using information to draw any conclusions at all. Perhaps it would be more effective to show what fallacious or irrational conclusions are being falsely drawn from this data and used to fire teachers, and then object to those specific instances of irrational actions. This value-added measure has not been shown to be intrinsically unreliable or wrongheaded but maybe some applications of it are.

</comment><comment><USER19> I'm working on reproducing the graph with the data available from the NYT, but I'm not sure on one or two details of the author's method. If someone sees it, please let me know! Things I can't tell so far:

1) How is a "teacher" defined? Just(hash firstname lastname)? If so...

2) When a teacher teaches multiple subjects per year, which one is chosen? Or are they both represented, so that "teacher" actually means (hash firstname lastname subject)?

<comment><USER20> If you want to see how I recreated the OP's graph, just fork my GitHub repo. It has R code and the data sets, too:

<https://github.com/tmoertel/nyva-cursory>

Anyway, here are the variables I used to identify comparable observations:

        ## these variables identify comparable teacher observations
        id_vars <- c("subject", "grade", "dbn",
                     "teacher_name_first_1", "teacher_name_last_1")

So I used subject, grade, school (identified by dbn) and the teacher's first and last names.

<comment><USER19> Nice, thanks for sharing. I used the same variables with the exception of dbn; my code is here <https://gist.github.com/4652968> (I later started applying filters such as 4th-grade teachers only, etc., which is reflected in the gist.)

I was pretty curious how the author specifically munged his data, since then we could put to rest the speculation about the degree of correlation.

</comment></comment></comment><comment><USER21> Looking at the correlation in students between year to year makes clear what's going on - [http://garyrubinstein.teachforus.org/2012/03/06/analyzing- re...](http://garyrubinstein.teachforus.org/2012/03/06/analyzing-released-nyc- value-added-data-part-iii/)

There's such a high correlation between an individual student's score from one year to the next, and the number of data points is so small, that trying to tweeze out the teacher's contribution in a statistically meaningful way is fairly hopeless.

What I'd like to see are correlates with a teacher's own scores on the tests of the material they're supposed to be teaching (oh you think they all can get perfect scores easily? Hah!) and whether teachers banned from giving homework do any worse, and whether dumping the enforced curriculum in favor of letting students study at their own pace makes any difference. Given how little what the teachers actually do seems to make, it would be logical to at least dump the things which make school dull and unpleasant.

</comment><comment><USER22> There is no objective way to measure teacher performance. Any evaluation method that can be written as a list of rules can and will quickly be gamed.

The thing is, it's easy to find out who the best teachers are. Simply ask the students, parents, and staff. They all know who the good ones and the bad ones are - and that can't be gamed.

<comment><USER23> Your claim makes no sense. If the evaluation method measures what we want teachers to do, then it, by definition, can't be "gamed": if the measurement is high, then the teacher is doing what we want.

Are you claiming that there's something special about teaching that makes teacher performance much more difficult, or even impossible, to quantify? If so, what is the point of teaching if one cannot measure results?

Your solution to "ask the students, parents, and staff" is precisely a measurement method (albeit a more qualitative than quantitative one), and moreover, one that can be gamed easily by anyone who's socially shrewd. Qualitative measures like that is exactly why we have so many crappy politicians.

<comment><USER22> You can't specify everything in the rules. For example, I know a case where management decided to hand out bonuses to the staff for minimizing inventory, because inventory costs money. The staff minimized inventory, all right, and got their bonuses. Meanwhile, the production line would regularly get halted because they'd run out of things like 5 cent resistors. It was a disaster.

The same company decided to rate programmers based on the bug list. A big chart was posted on the wall that showed the daily bug count. It wasn't a week before huge fights erupted over the bug count - over what was and was not a bug. The programmers quickly gamed it. They'd hide bugs, they'd refuse to fix one bug if that fix would produce some other minor bugs (e.g. if the bug was "feature X missing", then feature X is added, but had a couple issues with it, then X would not get fixed). They'd even add "bugs" blamed on other programmers and then "fix" them to get the credit.

Management gave up on that after two weeks and pulled the banner down.

<comment><USER17> For teachers, the metric is (roughly speaking) "% of students capable of multiplying/dividing numbers up to 4 digits in a standardized test setting". How do you game this metric?

The fact that one company used a couple of bad objective metrics doesn't mean all objective metrics are bad. They are used with a great deal of success in many fields. Sales people are paid on commission, traders are paid proportionally to (risk adjusted) profits, etc. All it means is that if you set the wrong goals for your company, you'll probably succeed at the wrong thing.

So tell us - is "maximize the % of students capable of multiplying/dividing 4 digit numbers" the wrong goal? If so, what is the right goal, and why can't it be measured?

<comment><USER22> One popular way of gaming the metric is systematic cheating on the tests by the teachers. I say popular because it has happened on a large scale, most recently in Atlanta as I recall.

Another way to manipulate the test results is to manipulate which students are in your class or your school.

The point is, people are endlessly creative in subverting rules to their own benefit - so they conform to the letter of the rules but not the spirit.

Consider also the "work to rule" technique used by unions as a bargaining tactic. It's as simple as the workers literally adhering to their job descriptions. It doesn't work out well for the company.

<comment><USER17> To prevent cheating, test administration should be handled by someone other than teachers.

The fact that the current system has a bunch of cheaters is not an argument against more carefully and objectively measuring the current system. What next - bankers sometimes engage in rogue trading, so we should reduce monitoring of their behavior?

 _Another way to manipulate the test results is to manipulate which students are in your class or your school._

This is very difficult with VAM, since the goal is to increase (actual score - statistically predicted score). You need to reliably identify students who will do better than their statistical predictor.

I.e., you need to discover students who will improve drastically _this year_ and then pack your student body with them.

</comment></comment></comment></comment></comment></comment><comment><USER24> The author's argument for this post is rather poor. He states that the raw data plot is noisy and weakly correlated, thus no relationship can be drawn by averaging the data into sets of buckets.

While the author is correct in that averaging hides the variance of data, he does not try to answer the question of "Can a trend be found from noisy data?" or show other accepted statistical methods that show no correlation in the data.

Instead the author dismisses the report from Gates through name calling: "It seems like the point of this 'research' is to simply 'prove' that Gates was right about what he expected to be true. "

</comment><comment><USER25> As far as I can tell, the author breaks the universe of teachers into 5% groups and then proceeds to show that the percentile groups are ordinally stable between these two years. In other words, the top scoring group in year 1 beat all other groups in year 2, and so forth, with perhaps some slight shuffling in the absolute middle of the distribution [hard to see on the graph].

This is supposed to be evidence that the correlation is weak??

</comment><comment><USER26> Even if Bill Gates isn't doing the best job, every time I see one of these articles, it appears that there isn't any advice on better ways to grade teachers. Did I miss that in the article? Are there a lot of other people in the field that are doing better work? (I would really like to read if anyone can provide links to papers to other ways of analyzing teachers)

<comment><USER27> _Did I miss that in the article_

The blog link to this thread is a propaganda site. It conspicuously doesn't reference any of the original materials that it is attempting (weakly) to refute.

There was an article on HN last week that referenced a more source material article about the project.

Here's the link to the METProject's web site: <http://www.metproject.org/>

<comment><USER26> Thanks

</comment></comment></comment><comment><USER28> I'm confused as to why the "'raw' score (for value added, this is a number between -1 and +1)" goes up to ~1.6 in 2009-2010 and up to ~1.1 in 2008-2009. Why does the data go outside the ranges he states? I find it hard to believe someone who can't read something so simple off his own graph.

<comment><USER19> The author incorrectly stated that "value added" is a score between -1 and +1. In fact, "value added" scores are z scores, which can in theory range from (-∞,∞).

</comment></comment><comment><USER8> To build intuition, let's consider a hypothetical society. We divide a group of people in two. The first group rolls a die with 100 sides labeled from 1 to 100 in even increments. The second group rolls a die with labeled 1 to 110 in even increments. The roll determines their annual ability level which is unknowable. If you were hiring, which group would you prefer? Is it fair to the second group?

Note that this isn't strictly equivalent for several reasons. The game above the error is part of the generating process instead of the measurement process. Also the distribution is district rather than continuous. The key commonality is that a weak predictor at an individual level can be a meaningful predictor at a group level.

<comment><USER13> To provide a contrary hypothetical...

Imagine if one group had 55% of its dice labeled up to 110 and 45% up to 100, and the other group had the opposite. So if all you use for hiring is the group membership, you're going to very arbitrarily miss out on a lot of 110s and hire a lot of 100s. And now also imagine that this process of identifying who is in what group is ridiculously expensive.

<comment><USER8> It's not contrary at all. It's the same point. The changing mix is merely a difference of degree. The key argument you raise is that discrimination has a cost. I don't have the numbers offhand to determine whether the cost of monitoring exceeds the benefit of higher quality education. Regardless, that's a different argument that should be backed by a different set of data.

<comment><USER13> It's contrary in that a naive interpretation leads to the opposite conclusion. That's all I meant. And I'm not sure how you define what is a different argument and what isn't. It's all about the value of these scores.

</comment></comment></comment></comment><comment><USER29> If you want to crunch the numbers yourself, here's the raw data: [http://www.ny1.com/content/top_stories/156599/now- available-...](http://www.ny1.com/content/top_stories/156599/now-available-- 2007-2010-nyc-teacher-performance-data)

</comment><comment><USER29> I don't know enough about statistics to judge the strength of Mr Rubinstein's critique, but I find this a little odd: The axes on his graph is a 'raw score' between -1 and 1, but the axes on the MET study graph is 'standard deviations'. Is that significant?

</comment><comment><USER30> More weekends than not, Colin shares here on HN an interesting link about education policy. I see from Colin's own top level comment that this one is shared for methodological discussion. I'm still mulling over what I think about this link after reading it, but I'm not sure I can agree that the Gates Foundation research group is engaged in a "lie" about anything. Education policy is the issue that drew me to participate on Hacker News,

<http://news.ycombinator.com/item?id=4728123>

and I'm glad to see that so many participants, from the founder on to the newest member, enjoy thinking about and checking facts on education issues.

There is other research on the issue of teacher quality and value-added measures to assess teacher quality,

<http://hanushek.stanford.edu/publications/teacher-quality>

and I encourage Hacker News participants to dig through some of the other publications to figure out what the best available current data show.

The other comments here suggest that the blog author of the submitted blog post is overstating his own case at least as much as he accuses the Gates Foundation supporters of overstating their case. If people who oppose the kind of teacher ratings proposed by the Gates Foundation really had courage of their convictions, they might try to let learners have full power to shop for teachers, on the grounds that teacher quality measures miss many dimensions of teacher performance that are important to individual learners. In fact, very few states even have as easy and time-proven a policy reform as statewide open enrollment (which my state has had for almost a generation now)

[http://education.state.mn.us/MDE/StuSuc/EnrollChoice/index.h...](http://education.state.mn.us/MDE/StuSuc/EnrollChoice/index.html)

and no state yet lets learners shop for schools on an equal per-capita funding basis whether the school is state-operated or not (as the Netherlands has for more than a century). Teachers will have plenty of deserved professional respect and regard from their clients if their clients have power to shop. But if policy proposals for learner power to shop are rejected, hand in hand with rejecting proposals for evaluating teachers for their effectiveness in publicly subsidized instruction, I wonder what the true agenda is. What assurance do we (we parents, we taxpayers, we members of the general public) have that all schools are staffed with the best available teachers unless someone is checking on how the teachers are doing their work?

</comment><comment><USER31> Typically when someone posts a baiting title like that I know not to trust them. Scholarship and evidence don't need hyperbolic headlines.

<comment><AUTHOR> I think you are mistaken. In today's attention economy even the very best scholarship and the very best evidence-based conclusions will be completely ignored unless there is a hook to get people, preferably lots of people, to read it.

Even here on the allegedly rational Hacker News I've seen item after item sink without trace, whereas others with significantly fewer details and significantly worse evidence get voted up and read by thousands.

Alex Bellos recently passed on to me what his editor told him. It doesn't matter how good your article is, if no one reads it, or if no one gets to the point, it's no use and a waste of your time.

I'd like to think "Scholarship and evidence don't need hyperbolic headlines." Sadly, I think that scholarship and evidence say otherwise.

<comment><USER32> When is HN alleged to be rational?

</comment></comment></comment><comment><USER33> Isn't the point that _before_ starting a measurement exercise one should have defined how one was going to interpret the results - and the whole is or is not successful if it meets its own success criteria

</comment><comment><USER34> So if the teacher evaluation method is alleged to be inferior, please provide a new evaluation method which is superior to it.

Can't? Won't? Then be quiet.

<comment><USER35> The idea would be not to waste numerous resources and money implementing a broken idea and spend some time coming up with a better one. Why put the education of our children and the careers of good teachers on the line with such a poorly thought out and half-assed idea?

<comment><USER34> If you think that no time has been spent coming up with this idea, you are coming very late to the party. This debate is decades old, at a minimum. Dates from 1971, says Wikipedia.

<http://en.wikipedia.org/wiki/Value-added_modeling>

It's not something that "Bill Gates" or anyone else made up yesterday. It's a state-of-the-art approach to a difficult problem. If you have a better way, let's hear it. Otherwise, be quiet.

<comment><USER13> You: "Yeah, okay, this method doesn't work well enough to accomplish anything and it's ridiculously expensive. HOWEVER, it's been used for decades, and I don't know any other methods that actually work. So let's continue pissing money down the drain."

</comment></comment></comment></comment><comment><USER36> This is the corporatist way. Everything is measured so it can be 'tweaked' by managers and technocrats because school is a business now.

Having a bad teacher to me doesn't matter when any kid can turn on his phone or laptop and watch free MIT lectures, free Stanford lectures, free Khanacademy lectures, free Android and iOS developer courses all over youtube, ect.

Gates obsession with teacher metrics would be better spent on building an entirely free university with worldwide standardized credits, so somebody in Pakistan can have their education credentials accepted should they start working overseas instead of being forced to drive a cab around Montreal while spending thousands to retake what he/she already learned.

<comment><USER27> _Having a bad teacher to me doesn't matter when any kid can turn on his phone or laptop and watch free MIT lectures_

Alternative self-study education is small compensation for having your child literally waste a school year in a teacher's class who has no clue how to keep control of the kids or desire to go over the material in class vs assigning everything for homework. In my daughter's case, her fourth grade teacher was too busy using that vaunted Internet access to check her facebook page.

Also, your "doesn't matter" argument would hold a lot more water if I didn't have to pay significant taxes to support such a lame public education system.

</comment></comment><comment><USER37> Never trust anybody who tries to explain statistics using Excel.</comment>


Hackers Breached Virginia Bank Twice in Eight Months, Stole $2.4M - <AUTHOR> https://krebsonsecurity.com/2018/07/hackers-breached-virginia-bank-twice-in-eight-months-stole-2-4m/ <comment><USER2> > According to the lawsuit, in June 2018 Everest determined both the 2016 and > 2017 breaches were covered exclusively by the debit card rider, and not the > $8 million C&E ("computer and electronic crime") rider

Jeez, insurance companies are all the same. Regardless if you're an individual or a bank with millions on the line... you get treated with the same slight of hands and nonsense interpretations of reality.

> those exclusions rules out coverage for any loss "resulting directly or > indirectly from the use or purported use of credit, debit, charge, access, > convenience, or other cards . .

How could a spear phishing campaign using malware that hijacked critical parts of the banks infrastructure not be part of the C&E coverage, and merely 'debit and credit'. The last part was merely how the money was exfiltrated. But the entire crime was the result of the intrusion.

This seems like an easy to win case to me. But who knows.

<comment><USER3> This is how legal arguments work when actual money is at stake. If there's a non-insane point of view that says you could interpret a clause in either direction one side takes one position and the other side takes the other position.

It's usually something similar to this, for example a policy with a clause saying we always cover if X and another clause saying we never cover if Y, when both X and Y are true. That kind of thing.

My favorite example along these lines is the insurance for the World Trade Center disaster, which hinged on a question of if the 9/11 attacks were one event, or two, since of course it was two separate planes taking off at different airports piloted by different terrorists.

No matter how much you plan ahead and try to use definitive language it's usually possible to end up in a spot where it's still a matter of debate.

In this case it's a lot of discussion of proximate cause (the phrase "but for" is the tell there) which is a standard feature of insurance claim arguments after some sort of major loss.

Typically what happens is each side assesses how close the other's argument is to compelling and then based on that both sides come to a settlement agreement.

<comment><USER4> 'no consumer could reasonably be misled into thinking vitaminwater was a healthy beverage'

People will argue anything.

<comment><USER5> Is that really the exact language they used in their briefs?

</comment></comment></comment></comment><comment><USER6> Some US financial institutions are incorporating cybersecurity disclaimers.

Case in point: ETRADE. Just received an update to the customer agreement. The definition of "Force Majeure Event" (unforeseeable circumstances) was updated to include cybersecurity incidents. Also this: ETRADE ... makes no representation or warranty of any kind ... with respect to security.

<comment><USER7> Jesus. The whole point of a bank is security. Otherwise we'd all keep it under the mattress. This boggles the mind.

<comment><USER8> I recently paid to have a car transported across Australia. The warranty excluded force majeure events, as you'd expect, but on the list along with flooding, riots and the like, was the ambiguous "accident". Surely "accidents" were exactly what I'd want covered with a car transporter?!

<comment><USER9> A bit over a year ago I had a car my father and I had spent 13 months restoring shipped from CA to VA by a high-end enclosed auto transporter. Four hours into the drive an axle bearing seized up and the trailer caught fire. Total loss of all six cars, with over $1.25M in total damages (excluding the trailer).

The logical maneuvering the insurance companies employed to avoid paying their shares would have been awe inspiring to behold if I was not personally involved and therefore caught in the middle of a devastating situation.

If I learned anything, it's that marketing B.S. and testimonials mean absolutely nothing when a transportation company is at fault after an accident. Also, always insure your classic automobiles with "agreed upon value" policies. This way you are covered to some reasonable fraction of your restoration outlay...otherwise you end up cry-laughing when the low-ball, hand-selected comparative values show up for significantly under the value of your receipts.

<comment><USER10> Agreed on the agreed-value policies. We unfortunately had a claim with a car covered by Hagerty and they couldn't have been more professional, courteous, or speedy in resolving the claim. (We were 0% at fault in the accident, but even if we had been, I suspect the treatment would have been the same.) Hagerty agent even followed up afterwards to see how we were doing and to express sympathy for the loss of our car.

</comment></comment></comment></comment></comment><comment><USER11> I'm on the bank's side of the lawsuit based on what I read in this article. They were covered under "computer and electronic crime" insurance. If the hacks don't fall under that coverage, what would?

<comment><USER12> > I'm on the bank's side of the lawsuit based on what I read in this article

Did you read this bit:

'The second exclusion in the C&E rider negates coverage for "loss involving automated mechanical devices which, on behalf of the Insured, disburse Money, accept deposits, cash checks, drafts or similar Written instruments or make credit card loans . . .."''

And never lose the opportunity to blame 'Russian' hackers.

"Foregenix .. determined the hacking tools and activity appeared to come from Russian-based Internet addresses .. according to the bank Verizon's forensics experts concluded that the tools and servers used by the hackers were of Russian origin"

They're clever enough to hack a bank but not clever enough to disguise their IP address.

<comment><USER13> Or they disguised the IP addresses to look like Russian IPs? Although I'm no hacker- anyone know hard that would be to do?

<comment><USER14> If you're going to build a botnet, it'll probably mainly be a bunch of Russian and Chinese machines. They've got the most WinXP instances still running without hardly any updates.

</comment></comment></comment></comment><comment><USER15> What's interesting to me about this is it seems like the hack still required physical presence to pull it off. The criminals had to actually visit hundreds of ATMs over the span of a holiday weekend to withdraw the cash

I suspect it had to have been people in on the scam because I don't see how you could conceivably convince strangers to withdraw cash for you at that scale without raising eyebrows

<comment><USER16> If a guy in an Indian call center can convince people that the IRS is about to have them arrested if they don't immediately pay their back taxes with iTunes gift cards, you can certainly convince people to withdraw money from an ATM and send it somewhere.

<comment><USER17> It seems more likely that the ATM withdrawers were just normal criminals already integrated into normal criminal organizations. Everybody gets a cut, but nobody takes too big a cut because violence and repeat business. Normal criminals love ATM stuff because it's quite low-risk.

</comment></comment></comment><comment><USER18> Verizon has a cybersecurity unit that can be subcontracted by outside companies? Interesting.

EDIT: [http://www.verizonenterprise.com/products/security/](http://www.verizonenterprise.com/products/security/)

<comment><USER19> It's hilarious that they don't have a certificate on their domain.

<comment><USER18> Good catch! I wonder why?

<comment><USER20> "Enterprise"

</comment></comment></comment></comment><comment><USER21> > _Verizon was hired to investigate the 2017 attack, and according to the bank > Verizon's forensics experts concluded that the tools and servers used by the > hackers were of Russian origin_

Wow. One incompetent company leading another incompetent company. What could possibly go wrong?

I don't have hope for these types of companies. Their security is a joke. Their industry security is a joke.

<comment><USER22> The security consultants that work for Verizon aren't the same folks that allowed the Yahoo/Oath credentials dump from half a decade ago.

Verizon has a reputable security consulting arm that competes with Bishop Fox, FireEye, Rapid7, NCC Group, and other recognized computer security firms. Verizon is a massive company and isn't just wireless and home internet.

<comment><USER23> However, I don't care how different or secure their security division is. If they're happy to run it under the Verizon brand they I will continue to assume they are incompetent monkeys and they deserve to loose business for this.

Either up your security so Verizon is finally considered a credible brand, or spin the security business off as a separate entity.

</comment></comment></comment><comment><USER24> It's as if these systems don't emit an audit stream, which when combined with the least bit of monitoring would have set off all sorts of red flags during these obviously anomalous events.

Such negligence tends to make me wonder if it's to leave open the possibility of some easy insurance fraud. In this particular case, that seems to have backfired with supposed hackers arriving first, and the insurer sleazily wiggling out of their own obligations.

At a past job, we ran thousands of shared linux servers for web hosting purposes. This was back in the early 2000s, and even then we had replaced all the installed shells with versions logging all interactive commands via UDP to a centralized syslog server. There was a simple IRC bot filtering the logs and echoing suspicious stuff into an IRC channel we monitored. Things like attempts to gain root, looking at /etc/passwd, lines starting with "./", running known irc bouncers or other script kiddie activities would be clearly visible and someone would intervene.

That was just a web hosting company with a small team and quite limited resources. I expect better from these national financial service providers, this is just pathetic.

</comment><comment><USER25> Initial malware that came in through a Microsoft Word Document... It's 2018 and everything that is old is new again

<comment><USER26> It never got old. Phishing+macros+lateral movement are still a _very_ significant vector. The industry exacerbates this by running with the feel- good "don't blame the user!" mantra.

At some point you really do need to give up on your fancy canaries, gateway and host IDS, perimeter blinky boxes, threat intelligence feeds, endpoint protection products, etc, and just start firing those in your employ who willfully and joyously thumb their noses at basic security hygiene.

<comment><USER27> > and just start firing those in your employ who willfully and joyously thumb > their noses at basic security hygiene.

Until it's your top salesperson who 2x'd the quarterly revenue target... I'd like to live in a world where everyone knew basic security hygiene, but we have to teach it first, not punish.

<comment><USER28> But then it can be over emphasized, and no one in your organization trusts any links or attachments because of phishing. Then it all becomes a horrible mess of skype/slack IMs with the actual links to Sharefile or Dropbox shares. Then you wave goodbye to async communication because everytime someone sends you a hyperlink they _absolutely need_ to know if you were able to get the file...

<comment><USER29> I have worked at financial companies where they get it right, and it is not a problem. Having crappy infrastructure and procedures is never an excuse for poor security.

</comment></comment></comment></comment></comment><comment><USER30> Am pretty curious what kind of "skeleton key" ATM card they were using to access all of the ATM's as different users. Lest they were posed as repair people and stood there with a laptop hooked in.

<comment><USER31> Generally in these cases spoofed cards + access to back end system. They just look like ordinary customers from the ATM perspective.

</comment></comment><comment><USER17> IANAL, but this bank needs a better general counsel. The contract says "big payouts unless ATMs are involved, in which case small payouts". Sure, in order to draw out the court case longer than a day, they'll make some vaguely plausible argument to ignore the plain language of the contract. Still, it would have been so much better to realize ahead of time that "we're a bank, tied to an ATM network, so our insurance should cover the use of ATMs too!"

</comment><comment><USER32> No mention of what was done when the policy was sold. Most insurance companies do a check to minimize their liability. I would think that the insurance company would do a PCI and whatever other audits are used to verify security of the financial institution before writing a policy. An audit (and corresponding mitigation) would save the bank money on their insurance cost.

<comment><USER33> No need to due diligence on a policy if you don't intend to ever honor it

</comment></comment><comment><USER34> wondering why i've to use 2fa (with a damn token) to access my inbank but there's no need of 2fa (on phone maybe?) to withdraw money from atm.

PS: do they seriously have a system that can turn off the need of entering the pin to withdrwa money? why?

<comment><USER35> ATM withdrawls are already two-factor - unless your ATM experience is very different to mine.

You need the card (something you have, factor 1) and the PIN number (something you know, factor 2).

<comment><USER36> I guess that is traditional 2fa that never occurred to me. Shouldn't we update that to include one-time passcodes like we do know for most things?

<comment><USER37> We live in a tech bubble. Most people don't use one time pass codes for anything.

</comment></comment></comment></comment><comment><USER38> It feels to me like the first incident should be covered and the second one should not. It doesn't seem fair to keep relying on insurance when you know you have a problem.

</comment><comment><USER39> I wish I knew how to do that

</comment><comment><USER40> Bullish on bitcoin.</comment>


We can't understand the problem without writing the software - <AUTHOR> https://twitter.com/sarahmei/status/861596049793728512 <comment><USER2> If only software thought leaders embraced this. It appears to be a facet of whatever mathematics underlies software, so it's not going away, and it cripples any hope of reliably estimating development time.</comment>


The Squirrel Wars (2007) - <AUTHOR> http://www.nytimes.com/2007/10/07/magazine/07squirrels-t.html <comment> m-i-l _" especially during the Thatcher-Major years, when the British government re- enthroned competition in Britain, the gray was left alone, and it extended its range, at the expense of the red"_

I've seen Thatcher blamed for pretty much everything that is wrong with the country today (and quite rightly so in my opinion) but I must admit this is the first time I have seen her connected to the demise of the red squirrels.

Anyway, I grew up on the edge of a small town in the south of Scotland, and have fond childhood memories of seeing the cute red squirrels playing in the pine trees outside my kitchen window, so it does sadden me a little to see grey squirrels in their place now.

One thing the article doesn't mention though is that part of the problem is habitat loss - the red squirrels particularly like to eat seeds from pine cones for example. And in my case most of the pine trees outside my old family home's kitchen windows were blown down in various storms over the years.

As an aside, I did have a problem in London a few years back with grey squirrels digging up my tulip bulbs. This is particularly surprising since I live on the fourth floor and just have a small balcony rather than a garden, so I don't quite know how they got there. But I saw them several times so I knew it was them. I felt like I was under attack and that they were taunting me. I was tempted to set up the solution described in "Militarizing Your Backyard with Python: Computer Vision and the Squirrel Hordes" [0] (although eventually went for the low tech solution of burying the bulbs below wire mesh).

[0] [https://us.pycon.org/2012/schedule/presentation/267/](https://us.pycon.org/2012/schedule/presentation/267/)

</comment><comment><USER2> > It is a war between rodents. Since the 19th century, gray squirrels, an > American import, have been overtaking Britain's native red squirrels and > claiming their territory.

The Redcoats are... going?

> Parker is a professional pest controller from Newcastle. He keeps 300 dead > grays in his freezer, seven of them skinned, waiting for the day he will > have time to cook them.

That's not some sort of regional thing, is it?

<comment><USER3> Unless a very broadly defined region, no. I knew a man in the Washington, DC, suburbs who got tired of squirrels getting into his bird feeder. He acquired a pellet gun and stocked his freezer. I assume, based on my few dealings with him, that he skinned the squirrels before freezing, and I'm pretty sure that he cooked them.

</comment></comment><comment><USER4> 2015 mini-update -> [http://www.mirror.co.uk/news/uk-news/red-squirrels-back- uk-n...](http://www.mirror.co.uk/news/uk-news/red-squirrels-back-uk- natives-5465745)

</comment><comment><USER5> > Landed gentry kept grays in cages [...] A Mr. Brocklehurst, who had brought > over gray squirrels from America, released two on his property near Cheshire > in central England.

> Parker had said he wanted me to shoot the squirrel — that grays were in > Britain was, after all, my fault as an American — and I did not want to.

I'd say it's more the fault of the squeamish toff standing next to him, given that his ancestors may well have been among the original importers of the greys.</comment>


A week of selling software under a "Name Your Price" model - <AUTHOR> http://www.irradiatedsoftware.com/blog/files/a_week_of_sizeup_sales_with_name_your_price.php

<comment><USER2> I think you will find that customers are much, much less sensitive to pricing issues than developers are. This has been the consistent experience of people on the Business of Software boards.

Really, the best advice I have ever gotten in my business was to get over the feeling that it was somehow unclean to charge money, and charge the highest amount I could say with a straight face. (I literally winced when typing in the price the first time. And when raising it recently. Apparently I care a heck of a lot more than my customers do.)

There are _significant_ ancillary benefits to charging more. In addition to not sending 16% of your income to the fine folks at Paypal, you can afford advertising.

I charge $30 when people who consider themselves my competitors charge $0, $10, and $22. They apparently think that means a customer doing a comparison between the two of us will choose them. I think that means that I can afford to spend more on ads than them every single time. This is a significant factor when Google AdWords is the major advertising mechanism in my niche.

<comment><AUTHOR> I appreciate the advice. There is a clear idealist (developer) vs pragmatist (business person) clash here that I may need to overcome to survive in this business.</comment></comment>


Show HN: Kalu – Calculator concept for long and inter-linked calculations - <AUTHOR> http://kushagragour.in/lab/kalu/

<comment><USER2> The name means "dick" in Finnish. Oh well, there are thousands of languages spoken in the world, can't check them all!

...Actually, that would be a damn useful site: doesthiswordmeansomethingdirtyinanobscurelanguage.com

<comment><USER3> I'm rather surprised that doesn't exist already, actually.

</comment></comment><comment><USER4> This is a pretty cool idea.

One thing that would make it more useful to me, though much more difficult to implement, is that when you click a reused value, it store a reference to that result, so if you change the calculations for that result, all the references change also.

For example, that way I could have some initial parameters up top, and use those in a complicated calculation, with the end result changing if I change those parameters.

<comment><USER5> Bingo. Then add plotting functionality for ranges of those values.

</comment></comment><comment><USER6> Pretty neat.

Curious if it's out of score or valuable to make the output/input behave more like a variable than copy/paste? e.g. line 1 is "2 + 3", so you click on the result, "5" and you use that in a new expression: "5 + 20". However, if you go and change the original line to "7 + 3" the second expression could update to "10 + 20"

<comment><USER7> This was the first thing I tested, and I think it would be extremely valuable if results could propagate through future equations like this. Change the one at the top and everything below updates.

<comment><AUTHOR> Yes, I thought about that. The issue lies just in UX. Some people could want to copy-paste value without propagation and other with propagation. How does the app enable both things in the best way is the question. Just a thought: Cmd+Click?

</comment></comment></comment><comment><USER8> @chinchang: If you replace the eval() with math.eval from [http://mathjs.org/](http://mathjs.org/) here

        result = eval(match[1]);

You'll get access to many more functions, including unit conversions.

<comment><AUTHOR> That thing is awesome! Thank you so much for the link :) I'll look into it.

</comment></comment><comment><USER9> I like it, I'm taking the AI for Robotics class on Udacity, and I have a chromebook as my primary machine, I'm going to bookmark this and likely use it most of the time. Does it support math functions like power, exponential, etc? and how?

<comment><AUTHOR> Yes, it does. Actually any JavaScript works. So you can do Math.pow, Math.sin etc etc

</comment></comment><comment><USER10> > "keep writing your calculations in JavaScript"

None of the Math.x functions work, e.g. Math.floor(2.5). Defining functions also doesn't work.

Looks promising though, I would use it for scratching project euler problems.

<comment><AUTHOR> Tried your example: Math.floor(2.5). Seems to be working on Chrome. Which browser are you using?

</comment></comment><comment><USER11> I really like this. The only issue that I found in my short time playing with it is that a/0 returns infinity rather than undefined. 0/0 does return NaN, though.

</comment><comment><USER12> Reminds me of [http://tydligapp.com/](http://tydligapp.com/) . I always thought it would make a great desktop app.

<comment><USER13> Calca has served me pretty well on the desktop: [http://calca.io](http://calca.io)</comment></comment>