Morelli Paolo wrote: >>I have to analyse some clinical data. In particular the analysis is a >>comparison between two groups of the mean change baseline to endpoint of a >>score. The statistician who planned the analysis used the ANCOVA on the mean >>change, using as covariate the baseline values of the scores. >>Do you think this analysis is correct?
Dennis Roberts <[EMAIL PROTECTED]> wrote: >NO! ... this is not a legitimate covariate ... a pre measure of the same >thing you are measuring latter as evidence of effectiveness Neither the question nor the response are all that clearly phrased, but when I interpret them according to my reading, I don't agree. For instance, if you're measuring pain levels, I don't see anything wrong with measuring pain before treatment, randomly assigning patients to treatment and control groups, doing a regression for pain level afterwards with the pain level before and a treatment/control indicator as explanatory variables, and judging the effectiveness of the treatment by looking at the coefficient for the treatment/control variable. Or is the actual proposal something else? Radford Neal ---------------------------------------------------------------------------- Radford M. Neal [EMAIL PROTECTED] Dept. of Statistics and Dept. of Computer Science [EMAIL PROTECTED] University of Toronto http://www.cs.utoronto.ca/~radford ---------------------------------------------------------------------------- ================================================================= Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =================================================================
