How to perform a meta-analysis of studies without a control group? I want to meta-analyse some studies which I've already collected and review. However, the studies did not used control groups, due to the types of questions used. How can I do the meta-analysis or which software can I use?
Briefly my problem is as follows:
I reviewed studies which the goal was to evaluate the perception of certain samples of their own behaviour.
For each study, the proportion of the sample which claims to adopt the behaviour in analysis, is equivalent to the effect size.
Do you have any idea how can I determine the average effect size?
Thank you 
 A: This is just a meta-analysis of proportions (or transformed values thereof). A couple articles discussing methods for this are:
Stijnen, T., Hamza, T. H., & Ozdemir, P. (2010). Random effects meta-analysis of event outcome in the framework of the generalized linear mixed model with applications in sparse data. Statistics in Medicine, 29, 3046-3067.
Chang, B.-H., Waternaux, C., & Lipsitz, S. (2001). Meta-analysis of binary data: Which within study variance estimate to use? Statistics in Medicine, 20, 1947-1956.
Zhou, X.-H., Brizendine, E. J., & Pritz, M. B. (1999). Methods for combining rates from several studies. Statistics in Medicine, 18, 557-566.
A reproduction of the analyses from Stijnen et al. (2010) using the metafor package in R can be found here: http://www.metafor-project.org/doku.php/analyses:stijnen2010
More examples can be found in the help files of the package. In particular:
http://www.rdocumentation.org/packages/metafor/functions/dat.debruin2009
http://www.rdocumentation.org/packages/metafor/functions/dat.pritz1997
If you intend on using the package, you probably also want to take a look at the paper describing the package in more detail: 
Viechtbauer, W. (2010). Conducting meta-analyses in R with the metafor package. Journal of Statistical Software, 36(3), 1-48. http://www.jstatsoft.org/v36/i03/
A: This is a meta-analysis of proportions. Just as you mentioned, the m-a of proportions is a little different than other types of meta-analysis- it includes studies that do not use controls. 
You can use R to do a meta-analysis of proportions. I recently made a tutorial on that on YouTube and shared my code on Github. This hands-on tutorial provides a step-by-step guide showing you how to conduct a full meta-analysis of proportions.The R script shown in the video is readily adaptable for you to use for your own analyses.
Check out the tutorial here: https://youtu.be/2wbXTFvaRnM.
Download my code here: https://github.com/wnk4242/meta-analysis-of-proportions
