longitudinal study
A research method that observes the same subjects repeatedly over a long period. Common in social sciences, medicine, and psychology.
This longitudinal study tracked the subjects' health over 20 years.
横断的研究 is a cross-sectional study that examines different groups at one point in time, while 縦断的研究 follows the same group over time.
Compound of 縦断的 (longitudinal) + 研究 (research). The term is a direct translation of the English 'longitudinal study' and is used primarily in academic contexts.