Panel data
Panel data tracks the same set of units across multiple time periods, combining cross-sectional and time-series dimensions in a single dataset.
Also known aslongitudinal data
See it move
The infographic is a stacked-bar diagram representing a panel dataset of 150 retailers tracked over eight years. Each annual layer adds 150 observations: Year 1 contributes 150, Year 2 another 150, and Years 3 through 8 a combined 900, producing 1,200 total observations (N = 150 × T = 8). Because the same firms reappear each period, fixed-effects models can absorb permanent unit-level differences and reduce omitted-variable bias.
Check yourself
A researcher tracks the annual carbon emissions of 80 manufacturing firms across 5 consecutive years. What type of data structure does this create, and what is the total number of observations?