Sometimes, due to limited/very few number of RCTs, researcher needs to combine data with Non-RCTs study for meta-analysis. But, combining dat from both types of studies may increase the heterogeneity and mean difference.
How one can plan data analysis method to combine RCTs and observational studies in the meta-analysis? What model will be used to combine data of RCTs and observational study?
Combining data from RCTs and observational studies is simply mixing apples and oranges. One should not combine RCTs with observational studies. It will be nothing but garbage in and garbage out.
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Hi, Kalpesh Panara, I suggest you better analyze them separately. As in the following article, it has only 5 RCTs (17 observational).
Kandula, P., Dobre, M., Schold, J. D., Schreiber, M. J., Mehrotra, R., & Navaneethan, S. D. (2011). Vitamin D supplementation in chronic kidney disease: a systematic review and meta-analysis of observational studies and randomized controlled trials. Clinical Journal of the American Society of Nephrology, 6(1), 50-62.
It depends on the outcome you are evaluating; for example if you are interested on performing a metaanalysis for prevalence, and you include RCT and observational studies to evaluate the prevalence of certain disease among a specific population, the fact of the different study methodology may not affect the overall effect. What I recommend you is to consider the outcome you are evaluating and assess if the result may change between RCT and observational studies due to bias. Also I recommend you to use I2 and Cochrane Q to evaluate heterogeneity to select the appropriate model.
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