Re: group data statistical functions

[John C Nash <nashjc uottawa ca>]

Having just retired from teaching such things for over 3 decades, I must 
admit feeling very tired from trying to get the "formulas" purged from 
textbooks.

The problem is that the grouped data can have descriptive statistics 
(and order statistics too) that are rather poor approximations to the 
actual values from raw data. Thus it is quite important that the user 
really does decide which approximation should be used. This is even more 
the case when the ranges of the bins are not equal --- and published 
statistics are VERY bad this way.

The data presented are integers, so the grouped and raw data should 
produce the same results, but we don't know a priori whether data 
supposedly at "2" is from integers or numbers anywhere in
(1.5, 2.5] or [1.5, 2.5) or [1,2) even.

A grouped descriptive statistic almost needs a page of documentation per 
number. The exam results on any question I gave to otherwise smart 
students on this topic were always <50%. It's not rocket science here. 
Once you realize what is going on, one can quickly figure out whether it 
is worth doing.

Sorry if this seems a bit negative, but the dangers are rather like 
providing working flying controls for the kid in the back of the 777.

Offline I can provide ways to do it pretty quickly.

JN