**Core Concept:** A case-control study is a type of observational study that involves identifying cases (individuals with a particular disease or condition) and selecting control subjects (individuals without the disease or condition) to compare the factors that may have contributed to the development of the disease or condition under study. The study compares the exposures or risk factors of cases to those of controls to determine which factors are associated with the disease or condition.

**Why the Correct Answer is Right:** The correct answer is **D**. A case-control study compares cases (individuals with a particular disease or condition) to controls (individuals without the disease or condition). The study aims to identify risk factors or exposures that may have contributed to the development of the disease or condition. The correct answer (D) highlights that the study design does not involve prospective follow-up of a population to identify cases and controls, as this is the nature of a cohort study.

**Why Each Wrong Option is Incorrect:**

A. The statement "involves following a group of people over time" is incorrect for case-control studies. This is actually true for cohort studies, where the focus is on following a group of people over time to identify cases and controls.

B. Case-control studies do not randomly select cases and controls. They identify cases and then select controls from the same population or source population.

C. Case-control studies do not rely solely on self-reported data. Careful attention is given to the accuracy and validity of data collected from both cases and controls, but the study does not solely rely on self-reported data.

**Clinical Pearl:** Understanding the differences between case-control and cohort studies is essential for designing appropriate studies and interpreting research findings. Case-control studies are often used to identify risk factors associated with a disease or condition, while cohort studies are used to evaluate the effect of exposures or interventions on the occurrence of diseases or conditions. Both study designs have their strengths and limitations, and choosing the appropriate study design depends on the research question and the resources available.