This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Classification, Coho Study, Subject name: Social & Preventive Medicine
All are disadvantages of Coho study except 
Select and explain. 
A. Coho study involve a large number of people, B. Coho studies are expensive, C. Recall bias, D. Attrition
C: Recall bias
Answer: C: Recall bias 
Explanation: Disadvantages of coho study Time consuming and Expensive Attrition - loss of follow up Hawthorne bias Ethical issues Not useful in rare disease Disadvantages of case control study Calculation of Odds ratio (Relative risk - more accurate than OR) Recall bias