Karl.....besides Cohen's oft-cited article: Cohen, J. (1983) The cost of dichotomization. Applied Psychological Measurement, 7, 249-253. ...a recent article sheds even further light on this practice:
MacCallum, R. C., Zhang, S., Preacher, K. J., & Rucker, D. D. (2002). On the practice of dichotomization of quantitative variables. Psychological Methods, 7(1), 19-40. ...........hope this helps........dale Dale N. Glaser, Ph.D. Pacific Science & Engineering Group 6310 Greenwich Drive; Suite 200 San Diego, CA 92122 Phone: (858) 535-1661 Fax: (858) 535-1665 http://www.pacific-science.com -----Original Message----- From: Wuensch, Karl L [mailto:[EMAIL PROTECTED]] Sent: Friday, January 31, 2003 12:25 PM To: Edstat-L (E-mail) Subject: Dichotomization 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> . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . ================================================================= . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
