I am planning to perform meta-analysis of side effects for a medication. The outcome is the number of people who experienced the side effect of interest out of the total exposed. The duration of follow up (weeks to years) and sample size of the studies (14-30000) vary. The incidence is in the range of 0.3 %. Do I need to transform the data and which form of transformation will be the best. Secondly which measure will be the most appropriate for meta-analysis.