**Question:** Selection bias is due to -

A. Incomplete randomization
B. Lack of consent among participants
C. Differential enrollment of subjects
D. Incomplete follow-up

**Correct Answer:** C. Differential enrollment of subjects

**Core Concept:**
Selection bias occurs when study participants are not randomly chosen from the target population, resulting in a study sample that is not representative of the overall population being studied. This can lead to inaccurate conclusions about the population due to the introduced bias.

**Why the Correct Answer is Right:**
Selection bias is caused by differential enrollment of subjects, where the study participants are not chosen based on a random sampling process. This means that the study participants are not representative of the target population, leading to an inaccurate representation of the population being studied.

**Why Each Wrong Option is Incorrect:**
A. Incomplete randomization (Option A) refers to the study design issue where randomization is not done properly, leading to unequal distribution of participants between study groups. This is not the same as selection bias.
B. Lack of consent among participants (Option B) refers to the situation where participants do not provide consent to participate in the study, which is a study conduct issue, not a bias type.
D. Incomplete follow-up (Option D) refers to the situation where participants drop out or lose follow-up during the study, which is a study conduct issue, not a bias type.

**Clinical Pearl:**
Understanding selection bias and its types helps ensure the validity and generalizability of research findings. In clinical practice, this knowledge is important for interpreting research studies and making evidence-based decisions. It is essential to choose study participants through randomization methods to minimize selection bias and ensure the study results truly represent the target population.