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in my meta-analysis I have studies with three kinds of data reports of RCTs which I want to integrate into one group with standardized effect sizes.

  1. studies reporting baseline and post-treatment values
  2. studies reporting raw change values (change score) and their standard deviation
  3. studies reporting adjusted change values from ANCOVA models

I understand that I can use the baseline standard deviation to standardize the effect size in case 2 (or use the change score standard deviation or transforming the change score standard deviation to post-treatment standard deviation).

My question: can I also use baseline standard deviations for standardization in cases 1 and 3 to make it consistent across studies? If not, why? Because the variance is reduced as opposed to post-treatment SDs there I overestimate my effect?

This question has been bugging me for a while, I appreciate any input. Thank you!

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