I am trying to manage a meta-regression in SPSS17 using the effect size as the dependent variable. I want to explore if my independent variables affects the effect size. Some small practical questions:
What is the minimum number of studies necessary for a meta-regression?
- Some people suggest at least 10 studies are required. Why not 20 or 5 studies?
- Is the total sample size an important consideration?
- Why would 10 studies with 200 patients be enough, but 5 studies with 400 patients not be enough?
Can I enter all three regressors at once and report the global model, or do I have to enter one regressor at a time and report 3 models each one separately?
- How does the correlation between the independent variables affects this choice?
- How does the number of the studies affect the number of independent variables that I should enter simultaneously?
Does the independent variable have to be a scale variable?
- The dependent variable (=effect size) is, of course, scale. The independent variable must be also scale, or could be ordinal or nominal?
How can I weight my effect size for sample size?
What is the preferable level of significance?
- Is p<0.05 still acceptable for clinical research in such an analysis?