**Core Concept**
A cohort study is a type of observational study that involves following a group of individuals who share a common characteristic or experience over a period of time. This study design is used to investigate the relationship between a potential risk factor or exposure and a specific outcome or disease.

**Why the Correct Answer is Right**
In a cohort study, participants are grouped based on their exposure or risk factor status, and their outcomes or disease status are observed and recorded over time. This study design allows researchers to examine the incidence of a disease or outcome in relation to the exposure or risk factor, and to estimate the risk or association between the two. For example, a cohort study might investigate the relationship between smoking and the development of lung cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** A case-control study is a type of observational study that involves comparing individuals with a specific outcome or disease (cases) with individuals without the outcome or disease (controls). This study design is used to investigate the relationship between a potential risk factor or exposure and a specific outcome or disease, but it does not involve following a group of individuals over time.

**Option B:** A cross-sectional study is a type of observational study that involves examining a population or group at a single point in time. This study design is used to describe the prevalence of a disease or outcome in a population, but it does not involve following individuals over time.

**Option C:** A randomized controlled trial (RCT) is a type of experimental study that involves randomly assigning participants to either an intervention group or a control group. This study design is used to investigate the effectiveness of a treatment or intervention, but it is not a type of observational study.

**Clinical Pearl / High-Yield Fact**
Cohort studies are particularly useful for investigating chronic diseases or outcomes that take a long time to develop, such as cardiovascular disease or cancer.

**Correct Answer: C. A cohort study involves following a group of individuals who share a common characteristic or experience over a period of time.**