There was two ANOVAS performed in this study. They completed a repeated measures
The factors were cognitive data was analyzed by function of drugs, placebo vs
risperidone, which had two levels and by time which had 3 levels, within participants.
Looking at the statistics provided in Table 1 for the variable AGE, can you tell what the
shape of the distribution is (negatively skewed, roughly symmetric, or positively
The shape of the distribution was positively skewed because the testable participants had
a higher mean average of 9.0 versus the mean of the untestable participants at 7.0.
On page 230, in the section on "Cognitive measures," the authors report that the partial
eta squared for the interaction between time and drug for the Cancellation Task is .16.
Interpret that value.
According to the value of partial eta squared np^2 =.16, approximately the Risperidone resulted
in a large effect om more correct detections than placebo on the Cancellation Task
Although the authors state in the "Study Participants" section on page 229 that the sample
size is 38, in two places the inferred sample sizes are different from 38.
On page 230, in
the section on "Cognitive measures", the authors report the results for the interaction
between time and drug for the Cancellation Task as
(1, 17) = 3.18,
232 in Table 2 the sample sizes are given in the footnotes.
What is the sample size
according to these two analyses?
The sample size is 34 because not everyone was able to complete cognitive testing.
On page 230, in the section on "Cognitive measures", the authors mention that they will
study the drug effects by looking at the interaction between time and drug.
In fact, they
hope for an interaction between the two.
Why is that?
In other words, why not just
report the main effect of drug?