How do cross-sectional studies differ from longitudinal studies?

Cross-sectional studies are characterized by their focus on observing a population at a single point in time. This approach allows researchers to analyze and compare different groups or variables simultaneously without considering changes over time. By gathering data from various subjects or populations at one specific moment, cross-sectional studies can provide a snapshot that reflects the current state of affairs regarding the variables of interest.

In contrast, longitudinal studies involve collecting data at multiple points over an extended period, allowing researchers to observe changes and trends over time. This key difference is fundamental to understanding how these two types of studies serve different research purposes. Longitudinal studies are particularly useful for examining dynamics, causality, and developmental trends, while cross-sectional studies are more suited for understanding a situation or demographic characteristics as they exist at a given time.

The other distinctions mentioned in the provided options do not accurately reflect the primary differences between cross-sectional and longitudinal studies. For instance, sample size and the number of research questions are not defining characteristics that set these two methodologies apart.