Hello everyone.. I am trying to do a meta analysis of studies which report Odds Ratio (OR). I also have some studies which have reported only "proportions" and not OR.
My question is - can i convert proportions to OR using 2 by 2 table? And then use it along with the other OR data for forest plot?
Hi, Bhavadharini Balaji Usually, for binary outcomes(2 by 2 table), odds ratios are calculated from the reported summary statistics or are directly extracted from the study.
Different measures makes the meta-analysis meaniless or difficult to do and interpret. Hence, for studies that have reported only proportions you are free to convert to odd ratios. Also, for continuous outcomes, standardized mean differences can be calculated and converted to odds ratios too as recommended by McKenzie JE, Brennan SE. Chapter 12: Synthesizing and presenting findings using other methods. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.0 (updated July 2019). Cochrane, 2019. Available from http://www.training.cochrane.org/handbook.
However, Metaprop is a useful command in stata for the analysis using proportion, if all are in proportion. Good luck
Hi In a software named comprehensive meta analysis you coudl input different values like odds ratio or risk ration and it will compute the final effect size of the studies.
Bhavadharini Balaji let's assume you have two odds ratios from two different studies A and B. The first from study A was 2.0 and the second from study B was 4.0. what meta-analysis does is simply the same procedure of calculating a weighted mean.
Suppose the sample size from study A was 100 and the second was 200, then the pooled ratio is just the weighted sum: [ (100/100+200) * 2 ] + [ (200/100+200) * 4 ] = 3.3. That weighted sum is the pooled odds ratio.
What works for odds ratios also works for any statistic.
I hope that answers your question.
Thanks to everyone who responded. I know how to combine OR for weighted/pooled OR. I was only wondering if we could convert proportions to OR using 2 by 2 table.
Bhavadharini Balaji proportions can be converted to odds ratios as follows:
Odds of an event are (p/1-p), where p is the probability of an event to occur (e.g odds of raining tomorrow)
Odds ratio is simply dividing two odds. If a study is reporting that drug A has probability of cure of 0.6 (60%), and probability of cure for b is 0.7 (70%), then the odds ratio is calculated as follows:
Odds of cure for A = 0.6/(1-0.6) = 1.5
Odds of cure for B = 0.7/(1-0.7) = 2.33
then Odds ratio comparing B to A = 2.33/1.5 = 1.55
Therefore, the final form will be:
(PB/1-PB) / (PA/1-PA)
Hope that helps
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