You can't take the log of a negative number. You need to take an absolute valute or other convert the number of non-negative.
Paul R. Swank, Ph.D. Professor, Developmental Pediatrics Medical School UT Health Science Center at Houston -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Dianne Worth Sent: Wednesday, June 18, 2003 1:02 PM To: [EMAIL PROTECTED] Subject: Logs of nonnormal distributions? It is my understanding that if the data distribution is positively skewed , one can take a log of the data. If it's negatively skewed, one should 'flip' it by adding 1 to the largest value, and a series of steps that are probably best explained as follows: Original values are 1-8. Add 1 to 8 = 9. FLIPX=9-X LOGFLIPX=LOG(FLIPX) LOGX=.903089 - LOGFLIPX where .903089 is the log of the original largest value (8). My question: What if my positively skewed data all have negative values, say from -1 to -7? Does the same logic/procedure still hold? Thanks, DW ---------------------------------------------------------------------------- -- Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! begin 666 ATT00077.htm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` ` end . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
