Longitudinal Data

Longitudinal data, sometimes called panel data, is a data that is collected through a series of repeated observations of the same subjects over some extended time frame – and is useful for measuring change. Longitudinal data effectively follows the same sample over time, which differs fundamentally from cross-sectional data because it follows the same subjects over some time, while cross-sectional data samples different subjects (whether individuals, firms, countries, or regions) at each point in time. Meanwhile, a cross-sectional data set will always draw a new random sample.