Hi Linda (or should I say Howdy Neighbor),
As I understand it, the problem with the Mean or Average Deviation is that
due to the use of the absolute value, it is a "terminal procedure". In other
words, it cannot be used in further calculations (which is something that we
would like to be able to do for inferential statistics, etc.). My lecture
notes about this material are available on the web at:
http://www.uwsp.edu/psych/stat/5/CT-Var.htm#II
Take care,
Mark
--- Mark Plonsky, Ph.D. 715-346-3961 wk ---
--- Psychology Dept. 715-346-2778 fx ---
--- University of Wisconsin 715-344-0023 hm ---
--- Stevens Point, WI 54481 [EMAIL PROTECTED] ---
--- http://www.uwsp.edu/psych/mphome.htm ---
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Friday, September 22, 2000 2:20 PM
To: TIPS
Subject: standard deviation
Greetings to all stats historians out there
A student asked today, upon starting discussion of the standard deviation,
why we do not simply use the average (mean) absolute value of the deviation
scores, rather than taking the square root of the sum of squares. Many
introductory stats texts provide no explicit rationale or history of the
standard deviation formula. The mean absolute value of the deviation scores
would seem to be a reasonable descriptive measure of the variability of the
scores.
TIA for any help you can provide.
Linda Tollefsrud
University of Wisconsin - Barron County
1800 College Drive
Rice Lake, WI 54868-2497
[EMAIL PROTECTED]
(715) 234-8176 ext. 5417
