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
Equal interval reduces which bias- 
Select and explain. 
A. Selection bias, B. Berkesonian bias, C. Interviewer bias, D. None
A: Selection bias
Answer: A: Selection bias 
Explanation: Bias may arise due to errors of assessment of the outcome due to the human element. 3 sources: subject variation, observer bias , bias in evaluation. Selection bias: cases and controls may not be representative of cases and controls in population. There may be a systemic difference in characteristics between cases and controls. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 81