Jim,
You may be right, but I took intro stats in the late 1980's and we learned
both forms (we used the Gravetter & Wallnau text). Another change that I've
seen in that time is a greater reliance on computers to do stats. Perhaps
it's simply easier now to get both versions and that makes folks a little
more open to using them.
Just guessing,
Larry
> -----Original Message-----
> From: Jim Dougan [mailto:[EMAIL PROTECTED]]
> Sent: Monday, September 25, 2000 9:30 AM
> To: Larry Z. Daily
> Cc: TIPS
> Subject: RE: Another Standard Deviation question
>
>
>
>
> Right - I know that. But, that has always been the case and we have only
> recently been using the "N" formula at all. Look back ten years and you
> will find that most texts never even introduce the "N" formula. McCall's
> 2001 edition (just released) still only uses the "N-1" formula.
>
> Apparently, other disciplines use N-1 as well. This is the first semester
> in which I have broken down and followed the text, using only the "N"
> formula at the start - and now my students are telling me they use N-1 in
> Chemistry and Biology!
>
> So - my question remains: Why the change? As I noted, I suspect it has
> to do with using the z-score formula for r. In response to an earlier
> note, it may be true that the z-score formula is more intuitive for the
> professor - but it is certainly not more intuitive for the students, most
> of whom have absolutely no idea what a "moment" might be. Raw score
> deviation formulas make sense for the students because they understand a
> deviation score. The z-score formula, just one step removed from the
> deviation formula, is sufficiently abstract to confuse the beginning
> student.
>
> -- Jim
>
>
>
>
> On Mon, 25 Sep 2000, Larry Z. Daily wrote:
>
> > The N version of the formula is a descriptive statistic - it simply
> > describes the current sample (or population). The N-1 version is an
> > inferential statistic and takes into account degrees of freedom
> and the fact
> > that I've estimated the mean of the population.
> >
> > Larry
> >
> > ************************************************************
> > Larry Z. Daily
> > Assistant Professor of Psychology
> > Department of Psychology
> > White Hall, Room 213
> > Shepherd College
> > Shepherdstown, West Virginia 25443
> >
> > phone: (304) 876-5297
> > email: [EMAIL PROTECTED]
> > WWW: http://webpages.shepherd.edu/LDAILY/index.html
> >
> >
> > > -----Original Message-----
> > > From: James D. Dougan [mailto:[EMAIL PROTECTED]]
> > > Sent: Saturday, September 23, 2000 4:00 PM
> > > To: [EMAIL PROTECTED]
> > > Subject: Another Standard Deviation question
> > >
> > >
> > > All of this standard deviation talk suggests it is a good
> time to ask a
> > > question which has been bothering me for the last couple of years.....
> > >
> > > Back in the "good old days" all (or at least most) of the
> undergraduate
> > > statistics texts taught the standard deviation using ther
> "N-1" formula.
> > > The "N" formula was perhaps mentioned in a footnote, but often not
> > > mentioned at all...
> > >
> > > Now, virtually all of the texts teach the "N" formula in the beginning
> > > under descriptive stats, then introduce N-1 later under inferential.
> > >
> > > I hate the new way of doing it, partly because I have to remember new
> > > formulas but more because it seems to confuse the students.
> > >
> > > Why the change? What was wrong with the old method?
> > >
> > > My guess is that using the "N" formula allows one to use the z-score
> > > formula for Pearson r (the z-score formula for r does not
> work if you use
> > > N-1, a fact I unfortunately discovered in the middle of a lecture
> > > demonstration...).
> > >
> > > But - why use the z-score formula for r? The old covariance
> > > formula is far
> > > more intuitive than the z-score formula. Yes - you can easily
> > > show how the
> > > product of z-scores works the same way as covariance, but
> students really
> > > don't grasp z-scores very well to begin with and it is hard for
> > > them to get
> > > the translation back from z to covariance.
> > >
> > > My guess is that texts want to use the z-score formulation
> for r because
> > > it makes a smoother transation into multiple regression. But (sigh) I
> > > don't think multiple regression really belongs in a 200-level
> intro stat
> > > course....
> > >
> > > Lots of room for answers and commentaries here....shoot away....
> > >
> > > -- Jim
> > >
> > >
> > >
> > >
> > >
> >
> >
>
>
