Best study is -
Ans-C Meta-analysiso Here are the different epidemiological studies with decreasing order of accuracy to test the association between risk factor and disease : -1. Systematic review and meta-analysis -->> Overall most reliable2. Randomized controlled trials (controlled clinical trails) - Most reliable individual study.3. Retrospective (Non-concurrent/historic) Cohort study.4. Prospective (concurrent) Cohort study.5. Case control study6. Cross-sectional study7. Ecological study
Case-control study
Cohort study
Meta-analysis
RCT