How good are UK universities? In his regular column, Michael Blastland says comparison is irresistible. But watch out.

We're bad, they're good, gotta change.

Can't help looking over our shoulders, can we, at the way the rest of the world behaves and performs? Comparison is compulsive.

And so we should. It would be surprising if we had the edge every which way.

But to state the obvious, people are different in different countries because they're different, if you see what I mean. That is, international comparisons are seldom like with like. Some pesky social or cultural difference gets in the way - and one simple metric doesn't show it.

A great example recently - of how obvious, but vital, differences go unnoticed in big debates - was how UK and US universities compare.

The standard story is: not well. US good, UK lagging. And a common metric is that, according to one ranking, the US has 13 universities in the world top 20 to the UK's four.

Writing in the London Review of Books, Howard Hotson picked a couple of differences between the US and the UK like, er… population.

Context doesn't come more basic. And it seems the UK is doing better than you would expect for a country of its size compared with the US. Do we expect Lichtenstein to have 13 universities in the world top 20? Basingstoke to have as many football teams in the Premiership as London?

Compare the two countries by how many universities they have in the top 30 instead of the top 20 and the UK looks better still - but not if you look, instead, at the Times Higher Education world university rankings.

Perhaps next most obvious is money. How much do they spend on their universities and what do they get for it? Here's just one way of making that comparison.

According to the latest OECD figures, the US spends about 3.1% of its income on tertiary education, the UK less than half that. But simple calculations suggest that people in the UK have about twice the chance of attending an elite university.

Convinced that the UK comes out on top after all?

It's a mildly entertaining game to wonder what stories we would tell to justify the quick but often bad conclusion suggested by a raw number

Maybe. But maybe you might also want to ask if a fantastically disproportionate amount of UK spending goes on its top four. That is, you might have the population of Denmark but still manage a university in the top 20 if you throw the Treasury at it and 10p a head at the rest.

So maybe we should compare not total spending but spending per student at the elite institutions.

And it doesn't stop there. We might want to make a distinction between domestic and overseas students, might want to take into account the fact that the US national income is bigger than the UK's, might want to be sure that charitable giving and endowments are included in the calculation of spending.

And we might want to say that this affects such a small number of people that we just don't care.

The key with international comparisons is not to rest easy. But resting easy is what simple comparisons encourage - and often what people want. Here's a league table, here's a ranking, here's the powerful single number that proves…

My favourite bad example is from an academic who came across data to show that Finland had no escapes from open prisons. This was at a time when the UK was in a tizz about people waltzing out. He later discovered the reason: they didn't classify this as escape in Finland, but "absent without leave".

Image caption US universities dominate the top spots in world rankings

Or there is the comparison of nurses per head of population, where a figure for UK population was divided by a figure for the number of nurses - obtained from the Department of Health in London. Unfortunately, health is a devolved responsibility, so, at that time, the DoH didn't count the nurses in Scotland.

It's a mildly entertaining game to wonder what stories we would tell to justify the quick but often bad conclusion suggested by a raw number - the policy, social or cultural reasons that explain the apparent Finnish lawfulness, for example - "so much more civilized, those Scandinavians, even in prison" - or the performance of US universities.

The conclusions you draw about university education are your own and won't necessarily be Howard Hotson's. Maybe you will decide that the amount spent on US universities is a consequence of their superior performance - that is, people pay more because they perceive US university education to be better - so spending follows performance rather than causes it.

Maybe you will decide that British universities are better than given credit for. Maybe you will want a lot more data about how they compare further down the league.

Comparisons, especially across borders, are rarely as conclusive as they seem. Howard Hotson's numbers now feel like a "duh" moment. And by that I mean to flatter him. Maybe the conclusion is never to underestimate our ability to overlook the blinkin' obvious in search of a quick answer.