Here are some other helpful materials for you to read through.

Examples of reviews that use subgroup analysis

http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD009779.pub2/pdf

http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD008893.pub2/pdf

http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD009517.pub2/pdf