What type of study involves observing systems in their natural state without manipulation?

An observational study is characterized by the observation of subjects or systems in their natural environments without any manipulation or intervention by the researcher. This approach allows for the collection of data as it occurs in real-life settings, providing insights into behaviors, occurrences, or phenomena as they exist naturally.

In observational studies, researchers may document events, survey responses, or behaviors, but they do not influence the conditions or variables of the study. This makes observational studies particularly valuable in fields where controlled experimentation may be difficult or unethical, such as in certain environmental or social research contexts.

The other types of studies mentioned have distinct characteristics that differentiate them from observational studies. Controlled studies involve manipulation of variables to establish cause-and-effect relationships, while experimental studies require manipulation and control of factors to test hypotheses. Theoretical studies focus on developing models and frameworks based on existing theories rather than direct observation of real-world phenomena.