The study of a population over time, as opposed to cross-sectional analysis which is limited to a single point in time. time-series analysis and panel studies are both examples. In general, panel surveys use individual-level data and time-series analysis uses aggregate-level data (see ecological association). However, the chief difference is that panel studies have a relatively large number of units studied over a small number of time points (maybe just two), whilst time-series data have a small number of units (maybe just one) and a large number of time points.
— Stephen Fisher
