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
In a controlled trial to compare two treatments, the main purpose of randomization is to ensure that- 
Select and explain. 
A. The two groups will be similar in prognostic factors, B. The clinician does not know which treatment the subjects will receive, C. The sample may be referred to a known population, D. The clinician can predict in advance which treatment the subjects will receive
A: The two groups will be similar in prognostic factors
Answer: A: The two groups will be similar in prognostic factors 
Explanation: Randomization is an effo to control bias and allow for compatibility. Theoretically, it is possible to assure compatibility by matching. But when one matches one can only match those factors which are known to be impoant. There may be other factors which are known to be impoant. (refer pgno:82 park 23 rd edition)