Relational Gompertz Fertility Model

The relational Gompertz model expresses any population's cumulative fertility schedule as a simple linear transformation of a fixed standard schedule, after both are mapped through a double-logarithm (gompit) transform. Developed by William Brass and given its widely used standard by Heather Booth, it characterizes the entire age pattern of fertility with just two parameters — α, which shifts the schedule earlier or later, and β, which controls how concentrated or spread out childbearing is. This makes it a robust tool for smoothing, fitting, and especially for correcting and estimating fertility from the limited and error-prone data common in developing countries.