Wallace:
The rest of our statistical procedures (correlations,
regression, anova) build on a foundation of "squared deviation" scores,
not average deviation scores. They all hang together as related
procedures. The average deviation is not related to these other
procedures.
Squaring the deviation scores does more than get rid of negative
signs; scores farther away from the mean get added weight. In the simple
series 1,2,3,4,5 (m=3), the absolute deviations scores are 2,1,0,1,2
(average = 1.2). The squared deviations are 4,1,0,1,4, which, when
summed (=10) averaged (=2) and squared rooted back to the original
units, equals 1.414 (larger than 1.2). That's about the extent of what I
teach about AD - I use it as a set-up to introduce squared deviation
scores en-route to the variance and SD. But, we can probably have
legitimate uses for the AD. Knowing that the average deviation score in
Intro Psych equals 10 can be a useful statistic in its own right.
============================================
John W. Kulig
Professor of Psychology
Plymouth State College
Plymouth NH 03264
============================================
"Eat bread and salt and speak the truth"
Russian saying.
-----Original Message-----
From: Wallace E. Dixon, Jr. [mailto:[EMAIL PROTECTED]
Sent: Tuesday, February 25, 2003 12:40 PM
To: Teaching in the Psychological Sciences
Subject: SD Woes
Speaking of z-score woes, does anyone know how psychology ended up
with standard deviations rather than mean absolute differences from
the mean. Is it just because of ease of calculation?
wedj
--
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Wallace E. Dixon, Jr. |
Chair and Associate Professor | Rocket science is child's play
of Psychology | compared to understanding
Department of Psychology | child's play
East Tennessee State University | -unknown
Johnson City, TN 36714 |
(423) 439-6656 |
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