Tools for Those Who Summarize the Evidence Base
I am conducting a meta-analysis on the effectiveness of an intervention on two outcomes (attitudinal and behavioral). The effect size measure is Cohen's d. After computing the Cohen's d, I want to proceed to subgroup analysis and meta-regression. I am looking for resources or answers to the 2 questions I came across below.
For instance, one moderator is "interactive approach VS didactic approach", and another one is gender (male VS female).
1) Referring to the Cochrane's Handbook (http://handbook.cochrane.org/chapter_9/9_6_5_1_ensure_that_there_ar... (http://handbook.cochrane.org/chapter_9/9_6_5_1_ensure_that_there_ar...), it stated that at least ten studies in a meta-analysis are required. Does this "10 studies" mean that there should be at least 10 data EACH for interactive approach and didactic approach respectively? Or just 10 studies included in the meta-analysis as a whole?
3) Some reviewers said individual-level moderators (e.g. percentage of male, mean age) cannot not be used to conduct subgroup analysis; only the study-level moderators (e.g. publication year, location of study) can be used. Is this always true? What is the rationale?
Thank you all for the patience and help in advance!