A longitudinal study measures:

A longitudinal study is specifically designed to observe the same subjects over repeated intervals of time. This approach allows researchers to track changes and developments within those subjects across different periods, providing insights into trends, patterns, and causal relationships over time. By repeatedly measuring the same individuals, researchers can gain a deeper understanding of how certain variables evolve and how they may influence outcomes in the long run.

This method is particularly valuable in social work research because it can help identify how specific interventions impact clients over time or how particular social phenomena may change. For example, researchers might look at the effects of a social service program on participants' mental health across several months or years, yielding more robust conclusions than studies that only capture a snapshot in time.

The emphasis on repeated measures of the same subjects distinguishes longitudinal studies from other methodologies that may focus on single moments or different groups at one time. This is why understanding the design and objectives of longitudinal studies is crucial in research methods specific to social work practices.