Dear All,
I would really appreciate your advice regarding the following. I have
a set of data (pre-post continuous scale as within subjects factor),
and 2 groups (experim. vs control)-as within subjects factor.
QUESTIONS:
1) I have read in some places that if you have pre-test scores, an
ANCOVA should be done, using pre-test as the covariate. I have done
some t-test on pre-test data between the 2 groups and they are not
different, so should the pre test scores be still used as a covariate or not?
2) I went through my positively variables to transform the ones that
were skewed, however this did not make them any better and Kilgromov
stat was still violated normality, as was skewness z-scores. As there
is no non-parametric test equivalent to a mixed design (as far as i
know) I am tempted to go ahead with the repeared measures anova ahead
leaving the data as it is! Is this a problem and how could I correct it?
3) I have therefore stuck with a 2x2 mixed design anova (on
untransformed data), with group (exp vs cont) as the between subjects
factor and time (pre vs post) as the within subjects factor.
In the output the Mauchly's test wasn't reported (see below)-is it
because there are only 2 levels to my factors? Is it a problem?
Mauchly's W: 1.000
Approx. Chi-Square .00
df 0
Sig. .
Greenhouse-Geisser 1.
Huynh-Feldt 1.
Lower-bound 1.
many thanks
Ioanna
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