Which of the following is a type of longitudinal research?

Trend analysis is a type of longitudinal research because it involves examining data collected at multiple points in time to identify patterns, changes, or trends over an extended period. This approach allows researchers to observe how certain variables fluctuate or evolve, which is a hallmark of longitudinal studies. By focusing on trends, researchers can draw conclusions about relationships and developments that occur across different time periods, making it a powerful method for understanding dynamic changes in behavior, attitudes, or other psychological phenomena.

In contrast, the other options represent different research methods that do not fit the longitudinal framework. For instance, a case study typically involves an in-depth exploration of a single individual or group at one point in time, rather than following changes over time. Available data analysis often uses existing data sets without a longitudinal aspect, focusing instead on the present data available. Content analysis involves systematically analyzing written, verbal, or visual communication, and does not inherently involve the examination of data over time.