Discrete-Time Hazard of Migration

The discrete-time hazard model analyzes the timing of migration when the data arrive in chunks of time — usually person-years — rather than as exact dates. Paul Allison's 1982 formulation showed that an event history measured in discrete periods can be analyzed by a remarkably simple device: expand each person into one record per period they are at risk, mark whether the move happened in that period, and fit an ordinary binary regression (logit or complementary log-log) for the conditional probability of moving. The baseline period enters as a set of terms capturing duration dependence — how the risk of moving rises or falls with time elapsed — and covariates can change from period to period. Because annual migration data are the norm in panels and registers, this person-period approach has become the standard event-history tool in migration research, sitting alongside the continuous-time Cox model and extending naturally to competing destinations and repeat moves. Its great practical virtue is that the entire apparatus reduces to a logistic regression any analyst can run.