**Core Concept**
A cohort study is a type of observational study where a group of individuals sharing similar characteristics are followed over time to assess the development of an outcome or disease. This study design allows researchers to examine the association between exposure and outcome, providing valuable insights into the potential causes of a disease.

**Why the Correct Answer is Right**
The major advantage of a cohort study is its ability to establish temporal relationships between exposure and outcome. By following a group of individuals over time, researchers can determine whether exposure to a particular factor precedes the development of a disease, thereby establishing a potential cause-and-effect relationship. This is particularly useful in identifying risk factors for disease and understanding the underlying mechanisms of disease progression.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cohort studies do not have the same level of internal validity as randomized controlled trials (RCTs) in establishing causality.
**Option B:** This option is incorrect because while cohort studies can be expensive and time-consuming, they are not inherently more prone to bias than other study designs.
**Option C:** This option is incorrect because cohort studies are not typically used to establish the efficacy of interventions, but rather to examine the natural history of disease.

**Clinical Pearl / High-Yield Fact**
Cohort studies can be classified into two main types: prospective and retrospective. Prospective cohort studies follow individuals over time from the present into the future, while retrospective cohort studies examine past exposures and outcomes from existing data.

**Correct Answer:** D.