**Core Concept**
Berkesonian bias, also known as Berkson's bias, is a type of selection bias that occurs in case-control studies, particularly in hospital-based studies. This bias arises due to the difference in admission rates for different diseases, where individuals with certain diseases are more likely to be admitted to the hospital than those without the disease.

**Why the Correct Answer is Right**
Berkesonian bias occurs because the hospital admission rates for different diseases are not equal, leading to an unequal distribution of cases and controls in the study population. This can result in an overrepresentation of individuals with certain diseases, which can distort the association between the exposure and the disease. For example, if a hospital has a higher admission rate for patients with diabetes, the case-control study may overrepresent individuals with diabetes, leading to an artificial association between the exposure and diabetes.

**Why Each Wrong Option is Incorrect**
**Option A:** Confounding factors can indeed affect the results of a case-control study, but they do not cause Berkesonian bias. Confounding factors are variables that are associated with both the exposure and the disease, whereas Berkesonian bias is due to the differential admission rates for different diseases.

**Option C:** Bias introduced by the investigator is known as interviewer bias or observer bias, which occurs when the investigator's knowledge of the patient's disease status influences their assessment of the exposure. This is not the same as Berkesonian bias, which is due to the hospital admission rates.

**Option D:** Patient recall bias or information bias occurs when patients inaccurately report their exposure history, which can lead to biased results in case-control studies. However, this is not related to Berkesonian bias, which is due to the differential admission rates for different diseases.

**Clinical Pearl / High-Yield Fact**
When conducting case-control studies, particularly in hospital-based settings, it's essential to consider the potential for Berkesonian bias due to differential admission rates for different diseases. This can be mitigated by using population-based controls or adjusting for the hospital admission rates in the analysis.

**✓ Correct Answer: B. Different admission rates for different diseases**