**Core Concept:** Bias in clinical research refers to systematic errors or prejudices that can influence the results of a study. In the context of hospital-based studies, bias can arise due to differences in disease prevalence between cases and controls attending the hospital.

**Why the Correct Answer is Right:** The correct answer is option C, "Selection Bias," because it describes the type of bias that occurs when the patients who choose to seek medical care at a hospital differ systematically from the general population in terms of their disease prevalence. As a result, the findings from these studies may not accurately represent the true prevalence or severity of the diseases in the general population.

**Why Each Wrong Option is Incorrect:**

A. **Selection Bias (Option A):** This type of bias is not the correct answer because it refers to the bias resulting from patients being selectively included or excluded from the study based on certain criteria. In the given question, we are discussing bias due to differences in disease prevalence between cases and controls attending the hospital.

B. **Performance Bias (Option B):** Performance bias occurs when the way a treatment is administered or monitored influences the outcome. In this question, we are discussing bias due to differences in disease prevalence, not treatment administration.

D. **Detection Bias (Option D):** Detection bias occurs when the way a condition is diagnosed influences the outcome. However, in this question, we are discussing bias due to differences in disease prevalence, not diagnostic methods.

**Clinical Pearl:** In clinical research, it is essential to design studies with appropriate control groups to minimize bias. This ensures that the findings are representative of the general population and can inform clinical practice and public health policies.

**Correct Answer:** C. Selection Bias