Data resulting from the observation of a population on a number of variables over time. Whenever observations are made more than once, the data is considered to be longitudinal.
Longitudinal Data
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References
Bijleveld, C. C. J. H.; van der Kamp, L. J. T.; Mooijaart, A.; van der Kloot, W. A.; van der Leeden, R.; and van der Burg, E. Longitudinal Data Analysis: Designs, Models and Methods. London: Sage, 1998.Referenced on Wolfram|Alpha
Longitudinal DataCite this as:
Weisstein, Eric W. "Longitudinal Data." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LongitudinalData.html