What defines observational studies?

Observational studies are characterized by the fact that researchers observe subjects in their natural environment without manipulating any variables. This means that data is collected based on what occurs naturally, allowing researchers to identify patterns, correlations, and outcomes that may arise from different factors present in the subjects' lives. Such studies are particularly valuable in situations where experiments would be unethical or impractical, such as studying the impacts of certain health behaviors on disease outcomes.

The essence of observational studies lies in their focus on real-world settings, where outcomes are measured based on the naturally occurring variations in exposure rather than any direct intervention by the researchers. This approach can yield insights into causal relationships, although it does have limitations in terms of establishing direct causation compared to experimental studies.

While the other choices touch upon aspects of research methods, they do not accurately describe the defining feature of observational studies. For instance, manipulating variables indicates an experimental design, relying solely on surveys would not encompass the full scope of observational approaches, and depending solely on retrospective analysis excludes the potential for prospective data collection that can also be part of observational studies.