Sampling moments in Q

I was checking over a colleague's Q code that computes moments of a sample distribution taken from a statistical population. I realized that population moments were being computed against the sample - very naughty! The lesson of this blog is to be careful using out-of-the-box Q functions like var against a sample distribution.

Let's take a look at an example

q)sample:3 4 6 7 10
q)var sample
6f

This is the population variance being computed against the sample - this is an inaccurate moment! Instead create your own high-order function to compute sample moments.

q)svar:{(sum d*d:x-avg x)%-1+count x}
q)svar sample
7.5

Simples!