It is always helpful to consult references to assist you when analyzing the data. One such reference is Finding What Works in Health Care, from the Institute of Medicine.
Here are their recommended steps when "synthesizing the body of evidence" (from chapter 4):
-"Use a prespecified method to evaluate the body of evidence"
Be sure to look at:
"risk of bias, consistency, precision, directness, reporting bias"
-"For bodies of evidence that include observational research, also systematically assess the following characteristics for each outcome: dose-response association, plausible confounding that would change the observed effect, strength of association"
-"For each outcome specified in the protocol, use consistent language to characterize the level of confidence in the estimates of the effect of an intervention"
-"Conduct a qualitative synthesis"
-Determine whether you will do a meta-analysis
(Eden et al., 2011, p. 158-9).
Another reference to consult when synthesizing evidence is the Joanna Briggs Institute's Reviewers' Manual.