stdevp( ) appears to be mislabeled

[Mike Elzinga]

(06-06-2016 06:23 AM)parisse Wrote:  This is inferential statistics, which is advanced statistics. Before teaching that, I'm strongly convinced that one should teach descriptive statistics, including of course mean and standard deviation of a statistical serie (like for example the grades of students or the height...). And here it is of course divided by N and it is straightforward to explain why, while it is not for the unbiaised estimator from a sample (and in general inferential statistics is much more complicated to understand than descriptive statistics and I don't think you can understand inferential statistics if you don't have already well mastered descriptive statistics). That's why I'm convinced that the good name in a math package (especially in a calc) should be the shortest if one divides by N (i.e. stddev) and I won't change that.
Of course I agree that the documentation or even the menu items should make the distinction the clearest possible, I think it's clear in Xcas, but this does not depend on me on the Prime.

The documentation for stddevp is very explicit; it says, "Returns the population standard deviation of the elements of a list or vector, ..."

However it uses the calculation for the sample standard deviation; it divides by N-1.

The stddev help says, "Returns the standard deviation of the elements of a list or vector, ..." It divides by N; so it is what we normally call the population standard deviation. but the help documentation doesn't clarify that fact.

If you kept the names but changed what they did - namely, divide by N-1 in stddev and by N in stddevp - then the only other change you would need to make is to add the word "sample" to the help documentation for stddev and have it say explicitly, "Returns the sample standard deviation of the elements of a list or vector, ..."

This would at least make the notation consistent with the help documentation and with the standards that others are using.

Descriptive statistics and inferential statistics are typically taught as a two-semester sequence at universities in the US. In fact, the Advanced Placement Statistics taught in high schools in the US is just such a two-semester, university-level sequence. We actually get into these issues very early in these introductory courses; so they are not considered so "advanced" as you seem to suggest. The distinctions between discriptive parameter calculations and sample statistics used to infer population parameters are addressed very early on in these courses.

If it is the speed of parsing instructions that you are worried about, then one should make names that differ up front, like popstddev and sampstdev; or pstddev and sstddev. I didn't discover that stddevp calculated with N-1 until I started using it and noticed something was not right. The help documentation is currently misleading. Better to make the calculation do what the help says it does.

Obviously it is not my call in deciding what HP does with its documentation and its names for functions. All I can do is turn to tools that make the teaching of subject matter easier.