Hi,
I am conducting a meta-analysis with just RCTs and I am interested in the changes between baseline and outcome assessments as a response to an intervention for two study arms.
For the most of my studies, I have just mean and SD values and nothing else. So, I am not able to calculate the correlation and then find the SD value of the changes. And, I could not find any thing about how I can find the SD of the changes using the mean and SD data of baseline and outcome assessment. There is a formula on the Cochrane handbook to combine the two subgroups SD to find a common one, that you can see in on the attachment. However, I am not so sure if this is a reasonable way to calculate the SD for the changes using this formula. If you have any information about that and inform me or suggest another way to solve my problem, I will be so pleased.
Kind Regards
You should not calculate the effect size via correlation. I think the best way in this situation is to calculate the mean difference between the baseline and after-treatment for both intervention and control groups. Then, you should use this mean difference as an effect size, and due to the presence of an equal number in baseline and after-treatment groups, you can sum the standard deviation and divide 2. An extra formula is not required due to an equal number of subjects.
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