COHORT QUANTUM AS A FUNCTION OF TIME-DEPENDENT PERIOD QUANTUM FOR NON-REPEATABLE EVENTS

The paper discusses translation formulae for time-dependent cohort and period quantum for non-repeatable events. Cohort quantum expressions are investigated for two cases: one in which period quantum, and another in which the sum of the period rates decreases linearly with time. In both cases the assumption is that period tempo does not change. Sufficient conditions are given for the situation in which the cohort quantum simply equals the period quantum measured at the time when the cohort reaches the mean age of the period schedule of age-specific rates, given that the period rate sum is a polynomial function of time. The paper takes up an issue which was unresolved in the article 'Translation formulae for non-repeatable events', which appeared in the July 1994 issue of Population Studies.