Take note of the study type. If all of the study types are retrospective or case studies, a meta-analysis may not be possible. Likewise, if you find that a lot of your studies involve only a small number of participants (e.g., fewer than 10), a meta-analysis may not be possible.

It is important to assess whether there are differences in study and patient characteristics across comparisons that affect the summary measures of treatment effects (odds ratio or hazard ratio) for the interventions of interest relative to an overall reference treatment. The decision to perform a meta-analysis should be based primarily on clinical judgment of whether differences among studies may affect the comparisons of treatments or make some comparisons inappropriate.