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
Basic types of biases in epidemiological study 
Select and explain. 
A. Investigation bias, B. Subject bias, C. Random error, D. Analyzer bias
A: Investigation bias
Answer: A: Investigation 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. (refer pg 83 park 23 rd edition)