To test the association between risk factor and disease, which of the following is the wakest study design -

Ans. is 'b' i.e., Ecological study To test the association between risk factor and diseaseo Most reliable, overall --> systematic review and meta-analysis of RCTso Most reliable individual study --> Randomized controlled trial.o Most reliable observational analytic study Coho studyo Least reliable study and least reliable observational analytic study --> Ecological study.