Which of the following statements about longitudinal studies is true?

Longitudinal studies are characterized by the collection of data at multiple points in time, which allows researchers to track changes and developments in the subjects being studied. This repeated measurement can provide insights into trends over time, the stability of characteristics, and the relationships between variables as they evolve.

By following the same group of individuals across different time intervals, longitudinal studies can also help establish temporality, which is crucial for making stronger inferences about cause and effect relationships. This differentiates them from cross-sectional studies, which gather data at a single point in time and cannot effectively track changes or infer causality over time.

The other options present concepts that do not accurately describe the nature of longitudinal studies, thus reinforcing why the statement about collecting data at multiple time points is the correct and defining characteristic.