On Thu, 13 Apr 2000 11:53:05 GMT, Chuck Cleland <[EMAIL PROTECTED]>
wrote:
> I have an ordinal response variable measured at four different times
> as well as a 3 level between subjects factor. I looked at the time
> main effect with the Friedman Two-Way Analysis of Variance by Ranks.
> That effect was statistically significant and was followed up by
> single df comparisons of time one with each of the three other time
> points (Siegel and Castellan, 1988, pp. 181-183).
> I would like bring in the between subjects factor now as I expect an
> interaction between this factor and the time effect. Could anyone
> suggest ways of doing this with the ordinal (0 to 3) response
> variable? I have already looked at the simple main effect of time
> within each group with the Friedman test, but I would like to test the
> interaction.
An "ordinal (0 to 3) response variable" has to give you a WHOLE lot
of ties. (As I have posted before,) For simple analyses, forcing the
rank-transformation is morely to do harm than good when you start with
just a few ordinal categories. Using the scores of 0-3 or using some
other rational scoring, you can probably be quite safe in doing the
two-way ANOVA -- safer, I suspect, than anything you can do with
ranking as the first step.
--
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html
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