What type of measurement design assesses the same group of subjects over multiple time points?

A longitudinal design is the correct choice because it specifically involves measuring the same group of subjects repeatedly over an extended period. This approach allows researchers to observe changes and developments within the subjects over time, providing insights into trends and long-term effects. The strengths of longitudinal design include the ability to establish sequences of events and causality, which can be particularly useful in social work research for understanding the dynamics of individual or group behavior and outcomes over time.

In contrast, a cross-sectional design provides a snapshot of a population at a single point in time, which limits the ability to draw conclusions about changes or trends. A case study design focuses on an in-depth analysis of a single case or a small number of cases, offering rich, contextual understanding but not necessarily facilitating long-term assessments across a larger cohort. Experimental design typically involves manipulating variables in a controlled environment to determine cause-and-effect relationships, which may not focus on the changes over time in a specific group of subjects. Thus, the distinctive feature of longitudinal design is its time-oriented approach, making it ideal for tracking development and change.