What characterizes a longitudinal study in psychological research?

A longitudinal study is characterized by its design that involves following the same group of participants over an extended period. This allows researchers to observe changes and developments within individuals over time, providing valuable insights into patterns of behavior, psychological changes, or the progression of specific traits or conditions.

By repeatedly measuring the same participants, researchers can assess how factors or outcomes evolve, helping them to understand causation and development rather than just correlation. This method is particularly useful for studying developmental issues or the long-term effects of interventions.

The other options do not align with the fundamental design principles of longitudinal studies. One-time assessments or simultaneous testing of multiple groups do not enable the tracking of individual changes over time; rather, they capture a snapshot of a specific moment. Solely relying on questionnaires for data collection does not define a longitudinal study since various methods could be employed, including interviews or behavioral observations, as long as they involve the same participants across multiple assessments.