At 01:39 PM 1/8/2007, you wrote:
My new stats class is underway and now that I look carefully at the
book (Aron et al) I see that their version of this formula is done
with a denominator of N, which in my opinion causes a
underestimation of dispersion and (for fact) will make my life a
living hell if I choose to go with it.
I had a similar situation with another text I used for stats, though
in that one they refer to "sample SD" using N and "estimated
population SD" using n-1. I believe the Aron et al. text introduces
the "population" formula (denominator of N) first and then several
chapters later introduces the "sample" formula (denominator of n-1).
Glancing at the 2nd edition, it looks like they briefly mentioned the
n-1 approach when first introducing the SD (ch 2) and then address it
in more detail in the scope of hypothesis testing and single-sample
t-test in ch 9. To me this adds to the confusion my students had
since several weeks after learning the formula for the SD they had to
learn a new formula for it... I would present both along with an
explanation of the difference and which one you would prefer. Also,
let them know if they go with the n-1 approach, then answers they
calculate for problems at the end of the chapters could be "off" from
what is given in the back of the book...
Good luck!
- Marc
=============================================
G. Marc Turner, PhD, MEd, Network+, MCP
Senior Lecturer & Technology Coordinator
Department of Psychology
Texas State University-San Marcos
San Marcos, TX 78666
phone: (512)245-2526
email: [EMAIL PROTECTED]
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