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
[{'content': 'Randomized study is done in people who are volunteer for the study. Which type of bias may occur ? \nSelect and explain. \nA. Hawthorne bias, B. Berkesonian bias, C. Selection bias, D. Attention bias', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Selection bias", 'role': 'assistant'}]