**Core Concept**
Ecological studies are a type of observational study that examines the association between exposure and outcome at the population or group level, rather than the individual level. This design is useful for investigating the relationship between environmental or policy-level factors and health outcomes.

**Why the Correct Answer is Right**
An ecological study is not considered an experimental study because it does not involve manipulating an independent variable to observe the effect on a dependent variable. Instead, it analyzes existing data to identify patterns and associations between variables. Ecological studies can be prone to biases, such as ecological fallacy, where associations observed at the group level do not necessarily hold true at the individual level. This design is often used to investigate the impact of environmental or policy-level factors on health outcomes.

**Why Each Wrong Option is Incorrect**
**Option A:** A Randomized Controlled Trial (RCT) is an experimental study design that involves randomly assigning participants to intervention or control groups to evaluate the efficacy of an intervention. RCTs are considered the gold standard for evaluating the effectiveness of interventions.
**Option C:** A pre-post clinical study is a type of observational study that involves measuring outcomes before and after an intervention or exposure. While it is not an experimental study, it is still a type of observational study, and its limitations should be considered when interpreting results.
**Option D:** A meta-analysis is a statistical analysis that combines the results of multiple studies to draw conclusions about a specific research question. While it is a type of systematic review, it is not a study design in itself, and the individual studies included in the meta-analysis may be experimental or observational in nature.

**Clinical Pearl / High-Yield Fact**
When evaluating study designs, remember that ecological studies are observational in nature and should be interpreted with caution to avoid ecological fallacy. Always consider the potential biases and limitations of ecological studies when drawing conclusions.

**✓ Correct Answer: B. Ecological study**