<prompt> To test the association between risk factor and disease, which of the following is the wakest study design -Case-control studyEcological studyCoho studyCross-sectional study  <response>: 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. 