**Core Concept**
Ecological studies, also known as ecologic studies, are a type of observational study that examines the associations between exposure and outcome at the population or group level, rather than at the individual level. This type of study is often used to investigate the effects of environmental or lifestyle factors on health outcomes.

**Why the Correct Answer is Right**
In ecological studies, the unit of observation is the group or population, rather than the individual. This means that the study examines the relationships between exposure and outcome at the level of the entire population, such as a country, city, or demographic group. For example, an ecological study might examine the relationship between air pollution and lung cancer rates in different cities.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ecological studies do not examine the relationships between exposure and outcome at the individual level.
**Option B:** This option is incorrect because ecological studies do not focus on the individual characteristics or behaviors of participants.
**Option C:** This option is incorrect because ecological studies do not typically examine the relationships between exposure and outcome at the level of a specific institution or organization.

**Clinical Pearl / High-Yield Fact**
It's essential to note that ecological studies have several limitations, including the potential for confounding and reverse causality. Additionally, ecological studies can be prone to the "ecological fallacy," which occurs when conclusions are drawn about individuals based on group-level data.

**Correct Answer:** C. Group or population.