Bad maths or my bad Japanese?


> 東京都はインフルエンザになった人の数を４１９の病院で調べています。１１月２０日からの１週間にインフルエンザになって病院に来た人の
> **平均は、１つの病院で１．８６人でした** 。平均が１人以上になると、流行が始まったと考えます。  
>  The Tokyo metropolitan area is investigating the number of people who got
> influenza in 419 hospitals. In the week beginning the 11th of November the
> average number of people who got influenza and went to hospital was 1.86 in
> one hospital. When the average exceeds 1 person an epidemic is considered to
> have started.

As a scientist, I see mathematics being butchered all the time in the media.
I'm wondering if this is another example, or whether my Japanese is wrong.

What is the average taken over? I would assume it is the average over the 419
hospitals, but then 平均は、 **１つの** 病院で１．８６人でした makes no sense to me. Why are
they talking about one specific hospital? Perhaps １つの means 'each' in this
case? I'm not aware of this as a valid translation though.

If I interpret this correctly then an average of 1.86 people per hospital per
week doesn't sound worth reporting to me. Maybe I also misunderstood 流行.

In summary, I'd be happy if １つの病院で wasn't there, but the numbers still sound
too small to be interesting, which makes me think I've misunderstood.




  1. About "1つの病院で"

This means "per one hospital", as you suspected, not "in one hospital". I
think this is a bit of bad writing; this would be clearer if it were written,
"1つの病院 **あたり** （で）". I think the source is [this
news](http://www3.nhk.or.jp/news/easy/k10011241291000/k10011241291000.html)
from NHK news easy version, and the [corresponding
version](http://www3.nhk.or.jp/news/html/20171130/k10011241291000.html) says,
'インフルエンザの患者は１つの医療機関当たり１．８６人'. (Note that, although a bit confusing, as a
native speaker I had no problem interpreting the sentence. Although it is
dependent on the context)

  2. Isn't 1.86 too low?

Again, you are making a correct observation. 1.86 does seem to be too low, but
"流行が始まる" means something other than you (and I, initially,) first imagine.

[This
graph](http://www.metro.tokyo.jp/tosei/hodohappyo/press/2017/11/30/11.html)
shows the past statistics of the influenza epidemic. Each year, the peak lies
at 30-40 /定点, so that's the amount we'll be dealing with in real epidemic.
What values > 1 signifies, on the other hand, is the _start_ of the annual
epidemic; "Hey guys, this season has come. We are beginning to be infected by
influenza, and soon it'll be more widespread" (Influenza is a disease that is
fairly rare in seasons other than winter). I haven't been able to find any
academic source that supports the threshold, but I think now we have the idea.




  1. About "1つの病院で"

This means "per one hospital", as you suspected, not "in one hospital". I
think this is a bit of bad writing; this would be clearer if it were written,
"1つの病院 **あたり** （で）". I think the source is [this
news](http://www3.nhk.or.jp/news/easy/k10011241291000/k10011241291000.html)
from NHK news easy version, and the [corresponding
version](http://www3.nhk.or.jp/news/html/20171130/k10011241291000.html) says,
'インフルエンザの患者は１つの医療機関当たり１．８６人'. (Note that, although a bit confusing, as a
native speaker I had no problem interpreting the sentence. Although it is
dependent on the context)

  2. Isn't 1.86 too low?

Again, you are making a correct observation. 1.86 does seem to be too low, but
"流行が始まる" means something other than you (and I, initially,) first imagine.

[This
graph](http://www.metro.tokyo.jp/tosei/hodohappyo/press/2017/11/30/11.html)
shows the past statistics of the influenza epidemic. Each year, the peak lies
at 30-40 /定点, so that's the amount we'll be dealing with in real epidemic.
What values > 1 signifies, on the other hand, is the _start_ of the annual
epidemic; "Hey guys, this season has come. We are beginning to be infected by
influenza, and soon it'll be more widespread" (Influenza is a disease that is
fairly rare in seasons other than winter). I haven't been able to find any
academic source that supports the threshold, but I think now we have the idea.

