Dear r helpers,

I would like to look at the interaction between two two-level factors, one
between and one within participants, after accounting for any variance due
to practice (31 trials in each of two blocks) in the task.
It seems to require treating practice as a covariate.

All the examples I noticed for handling covariates (i.e. ANCOVA, including
the ones in Faraway's "Practical regression and anova using r") use lm(),
but this doesn't handle repeated-measures.

I thought of a solution in the form of first running a regression on the
covariate:
> cov.accnt = lm (myMeasure ~ myCovMeasure, data=dat)

and then run the aov() on the residuals:
> m.aov = aov (cov.accnt$residuals ~ withinVar*betweenVar +
Error(subj/withinVar, data=dat)

Does it seem to be a valid answer to my problem?

Is there an existing function that can do this (perhaps more appropriately)?

Thank you for any help,
dror

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