Which of the following research methods is used in the study?

A case study involves an in-depth analysis of a single individual or group, providing detailed qualitative data but lacking the ability to determine causal relationships due to its non-experimental nature. While it can offer insights into specific phenomena, it does not allow for manipulation of variables or control needed to establish causation.

Naturalistic observation entails observing subjects in their natural environment without manipulation or control by the researcher. This method provides valuable descriptive data but does not allow for the establishment of cause-and-effect relationships due to the absence of experimental manipulation.

Correlational research examines the relationship between two or more variables to determine if they are associated. However, this method does not involve manipulation of variables and cannot establish causation; it merely identifies patterns or trends in data without confirming if one variable causes changes in another.

Longitudinal research involves studying the same subjects over an extended period to observe changes and developments. Although it can provide insights into trends and patterns over time, it does not involve the experimental manipulation of variables necessary to establish causal relationships, which distinguishes it from experimental methods.