There is an excellent paper on median splits by MacCallum et al. in Psychological Methods, 2002, 7, 19-40.
There is also a equally good paper by Julie Irwin and Gary McClelland in a marketing journal. It either just came out or it is in press. (I couldn't find it with PsycInfo, so it may not be out yet.)
Both papers agree with Karl's advice. "When you think about a median split, DON'T."
Dave Howell
At 03:24 PM 1/31/2003 -0500, Wuensch, Karl L wrote:
When interested in the relationship between two continuous
variables, some researchers will dichotomize one of them prior to analysis.
I generally discourage such dichotomization, but the practice is common. A
colleague asked me today about the practice of dichotomizing by a median
split (top half versus bottom half) versus the practice of using only the
tails (bottom third versus top third, for example). I outlined my thoughts
on this matter and noted that I vaguely recall having read an article or two
on this matter long ago, but cannot put my finger on the article(s). Can
any of you all?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Karl L. Wuensch, Department of Psychology,
East Carolina University, Greenville NC 27858-4353
Voice: 252-328-4102 Fax: 252-328-6283
mailto:[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
http://core.ecu.edu/psyc/wuenschk/klw.htm
<http://core.ecu.edu/psyc/wuenschk/klw.htm>
.
.
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