This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
A researcher wants to (to a study of blood levels of lipids among people who smoke and those who do not. But he is now concerned that the smokers might differ from non-smokers in their diet, exercise, etc as well. This concern is known as: 
Select and explain. 
A. Recall bias, B. Information bias, C. Selection bias, D. Interviewer bias
C: Selection bias
Answer: C: Selection bias 
Explanation: Ans: C. Selection bias(Ref Park 24/e p78, 88, 23/e p73, 22/e p71; en.wikipedia.org/wiki/Bias_(statistics); http://sphweb. hume.hu.echdollt/mph-modules)Selection bias:Groups to be compared are differentially susceptible to outcome of interest, even before experimental maneuver is performed.Also referred as "Susceptibility bias".In the given question, researcher is concerned that the smokers might differ from non-smokers in their diet, exercise, etc.Hence, this concern is known as selection bias.