Joseph Coveney !!!kindly!!! showed that in fact I can use ANCOVA in a
within-subjects design. His .do file would be a nice addition to
Higbee's ANOVA FAQs on the Stata site, once I help with the equivalent
MANOVAs.
It is very typical of people in my field to still use ANOVA rather than
MANOVA for repeated measures analysis. Nor do I often seen mixed model
approaches that allow modeling the covariance structure explicitly,
like in SAS Mixed or R LME/NLME, despite the benefits of these
approaches. I have read enough about the disadvantages of ANOVA that I
have spent some time learning the basics of MANOVA and procedures like
R LME for repeated measures. I hope it pays off.
In my behavioral experiment, I have 2 levels in each factor I've
manipulated. So for some analyses, use of ANOVA or MANOVA is equivalent
since sphericity is always met if all factors have 2 levels.
-Dave
I believe that you *can* use the -continouous()- and -repeated()-
options
together. With involved models, you might need to explicitly specify
the
between-subjects error term using the -bse()- option, but that's not
any
impediment. I've illustrated their combined use in the do-file below
using
the two repeated-measures ANCOVA examples from Chapter 10 of B. J.
Winer,
D. R. Brown & K. M. Michels, _Statistical Principles in Experimental
Design_
3rd Edition. (NY: McGraw-Hill, 1991), pp. 820-36. The first example
has a
single time-invariate covariate for each individual; the second has a
time-varying covariate (i.e., the covariate has a different value at
each
repeated measurement). Note that the two examples in Winer, Brown &
Michels
don't need the -repeated()- option, since they both have only two
observations.
I'm not sure why Stata Corp. recommended considering -manova- to
David, but
perhaps it's because of the admonition stated in the preface to the
repeated-measures ANCOVA section from Winer, Brown & Michels (Section
10.5,
p. 820), "In the behavioral sciences area, the covariance matrix for
the
repeated measures is very likely to be more complicated than the
corresponding covariance structure assumed for the usual split-plot
design
[in agricultural research]." David's original posting related to the
area
of schizophrenia and sensorimotor inhibition.
Joseph Coveney
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