On Thu, 13 Apr 2000, Rich Ulrich wrote:
> 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.
>
Good point Rich. I didn't think about ties. If the ordinal data are
generated by having people rank order objects, you could avoid completely
ties by simply disallowing tied ranks. But in the situation Chuck
described (time as the repeated measure), there may well be a LOT of
ties, as you say.
Cheers,
Bruce
--
Bruce Weaver
[EMAIL PROTECTED]
http://www.angelfire.com/wv/bwhomedir/
===========================================================================
This list is open to everyone. Occasionally, less thoughtful
people send inappropriate messages. Please DO NOT COMPLAIN TO
THE POSTMASTER about these messages because the postmaster has no
way of controlling them, and excessive complaints will result in
termination of the list.
For information about this list, including information about the
problem of inappropriate messages and information about how to
unsubscribe, please see the web page at
http://jse.stat.ncsu.edu/
===========================================================================
