Regression to the mean is the tendency for an unusually high or low value to be followed by a measurement closer to the average.[^1] It is ubiquitous in repeated measurements. In panel data, the effect is stronger when selected units are far from their group mean and when serial correlation is low: the baseline may reflect a transitory swing. [^1]: Barnett, A. G., van der Pols, J. C., & Dobson, A. J. (2005). Regression to the mean: What it is and how to deal with it. *International Journal of Epidemiology*, 34(1), 215–220. > [!info]- Last updated: June 11, 2026