This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
Non - bias study is - 
Select and explain. 
A. Case control study, B. Coho study, C. Randomized controlled trials, D. Unrandomized trials
C: Randomized controlled trials
Answer: C: Randomized controlled trials 
Explanation: .<p>randomised control trials mainly include dtrawing up a protocol,selecting reference and experimental populations ,randomisation,manipulation or intervention ,follow up, assessment of outcome.RCT s are generally described as non biassed studies as they give no chance of any systemic error in the determination of association between exposure and disease.</p><p>ref:park&;s textbook of preventive and social medicine,22 nd edition ,pg no 70</p>