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: Dental
Berkesonian bias in a case control study is a bias due to: 
Select and explain. 
A. Presence of confounding factors, B. Different admission rates for different diseases, C. Bias introduced by investigator, D. Patient can not recall or gives false information
B: Different admission rates for different diseases
Answer: B: Different admission rates for different diseases 
Explanation: None