What does a longitudinal study primarily measure over time?

A longitudinal study is designed to observe the same subjects repeatedly over an extended period, which allows researchers to assess continuity and changes within that specific group. This approach is particularly valuable in developmental psychology as it provides insight into how individuals evolve over time, helping to track the progression of behaviors, traits, and skills within the same cohort.

By focusing exclusively on one group, longitudinal studies can reveal patterns and trends that highlight the influence of various factors on development while controlling for cohort effects that might skew comparisons across different groups. This makes it possible to gain a deeper understanding of individual development rather than just snapshots of different cohorts at various stages, which would not capture the nuances of change over time.