you may need to select a single effect size measure to use in your meta-analysis. You can choose the most commonly reported measure among the studies, or the one that is most appropriate based on the nature of the outcome and the research question.

If you need to convert between different effect size measures (e.g., OR to RR), you can use established formulas or online calculators.

Here are some common conversions: Converting Odds Ratio (OR) to Risk Ratio (RR): RR = OR / (1 - P0 + (P0 * OR)), where P0 is the incidence of the outcome in the unexposed group.

Converting Risk Ratio (RR) to Odds Ratio (OR): OR = RR / (1 - P0 + (P0 * RR)), where P0 is the incidence of the outcome in the unexposed group.

If you choose to convert all effect sizes to odds ratios (OR) for meta-analysis, you'll typically use a meta-analysis method designed for binary outcomes, such as the Mantel-Haenszel method or the DerSimonian and Laird method. These methods are commonly used for pooling odds ratios from individual studies.

I agree with Heba Ramadan, choose either RR, OR or Hazard ratio (HR), depending on what makes most sense and what is more applicable for your research question and commonly reported measures in that field. For some cases, OR or Hazard ratio may be more applicable, while RR is much more intuitive to interpret.

Check out this material for more info:

Article What’s the Risk: Differentiating Risk Ratios, Odds Ratios, a...

https://bookdown.org/MathiasHarrer/Doing_Meta_Analysis_in_R/pooling-es.html#binary-outcomes

Thanks, Danko for reinforcing what Heba said as well as sharing the two related articles!@ Danko Jeremic

In the same context, I would like to ask how we can convert the hazard ratio to probabilities. I have read some literature suggesting that P=HR/ (1+HR)

Is that correct?

another formula is P=100*(1-HR) which is inappropriate in the case of HR exceeding 1

thanks

IS