Which of the following describes a cross-sectional research design?

A cross-sectional research design is characterized by the measurement of all variables at the same time, which allows researchers to analyze data collected from various subjects or groups within a specific time frame. This approach provides a "snapshot" of the variables of interest, facilitating comparisons across different populations or groups and helping identify relationships or trends without the influence of time.

In contrast, the other options describe different research methodologies. The repeated measurement of variables over time indicates a longitudinal design, which tracks changes and developments in subjects over specified intervals. Longitudinal studies typically aim to understand how variables evolve rather than providing simultaneous comparisons. If data is consistently collected from the same subjects, it reinforces the longitudinal approach, which focuses on temporal sequences rather than static comparisons. Finally, measuring only one variable over time suggests a simplistic approach that does not harness the breadth of information available in a cross-sectional study, where multiple variables can be assessed at once to enhance understanding of complex relationships among them.