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Biology

Age-Period-Cohort Effects in Longitudinal Demographic Data

Quick fact

In any longitudinal dataset, age, period, and cohort are perfectly linearly dependent (Period = Age + Cohort), which means that without imposing additional assumptions, it is mathematically impossible to uniquely estimate the separate effects of all three.

Why this is interesting

We all know that people change as they age, but did you know that the year you were born can shape your life just as powerfully—and that demographers cannot easily tell the two apart?