Is there a name for that phenomenon? I saw a similar thing in some data that we were looking at recently, and it took a while to work out that the reason why one group's number was consistently a bit smaller than another group's number was that we were simply taking the max of a smaller group. it's obvious in retrospect, but can catch you out if you're not expecting it.
I'd like to have a name for it, a reference to send people to.
I think this[1] Stats StackExchange answer frames it well.
[1]: http://stats.stackexchange.com/questions/129885/why-does-inc...
> I believe that the Law of Large Numbers explains why the variance (standard error) goes down when the sample size increases. https://en.wikipedia.org/wiki/Law_of_large_numbers
So what I was looking at is the inverse of the law of large numbers.
It's probably a combination of genetics, cycling everywhere and eating so many slices of brown bread and potatoes.
Basic statistics also plays a part: when comparing arbitrary groups you'll often see smaller groups as outliers. Both high and low. Dutch population isn't huge (16m) so that is also a contributing factor..