Takes place over a long period of time with just one test subject.

• A. Cross-Sectional Studies
• B. Meta-Analysis
• C. Case Studies
• D. Longitudinal Research

Answer: (D)

Tracking a single individual over an extended period to observe how they change over time is the hallmark of longitudinal research. This design follows the same subject across multiple time points, letting you see development, trends, or causal sequences as they unfold. In contrast, cross-sectional studies compare many different individuals at roughly the same time, providing a snapshot rather than a timeline. A case study focuses in-depth on one person (or a small group) and may or may not span a long period, but isn’t defined by repeated measurements over time. A meta-analysis combines results from multiple separate studies to draw broader conclusions rather than collecting new data from a single subject. Therefore, the description best fits longitudinal research.