Question regarding Effect Sizes
- From: quebecstat <probameasure@xxxxxxx>
- Date: Sat, 24 Feb 2007 20:47:18 EST
A researcher recently asked me to do a piece of work for him.
He has data (one variable about pain) on subjects from three groups: two treatment groups and one control group. There are two timepoints.
He said he is interested in computing "within group and between group effect sizes". That does not make much sense to me as an effect size is for me the effect of a treatment.
I am thinking I can compute
1/The effect size of the first treatment group with the control group.
2/The effect size of the second treatment group with the control group.
I read that an effect size is computed as a standardized difference between two means. But here, I have two timepoints. So, how should I compute those effect sizes?
Should I first compute the improvements in pain (an improvement can be negative) from time 1 to time 2, then compute the mean improvements for each group, then compute the standardized difference in mean improvement and call that the effect size?
many thanks for your help.
.
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