[docs] Make the documentation for statistics' data argument clearer. (issue 27825)

[Steven D'Aprano]

On Fri, Oct 14, 2016 at 04:18:30PM -0000, mariatta.wijaya at gmail.com wrote:
[...]
> I've been working on another patch that will address other comments
> above. But since I'm not a statistician, I'm a bit stumped on how to
> improve this particular example about median_grouped().

Okay, I'll work on that particular example.

Thanks for your help and I look forward to the revised patch!

-- 
Steve