ISSUES IN MODELLING

The major issues in population studies are as follows:

• growth of population;

• changes in composition of population; and

• demographic processes such as nuptiality (i.e., marriage), fertility, mortality and migration.

Mathematical and statistical models have been used in studies of all the above issues. Among them, as compared to nuptiality, more attention has been paid to modelling of fertility and mortality.

PREDICTING GROWTH OF POPULATIONS AND SUBPOPULATIONS

Mathematical models have been used commonly to predict the size and composition of population of a country or a geographical region. For this purpose, various functions such as linear function, geometric or exponential growth function, modified exponential function, logistic curve, Makeham curve, Gompertz curve, polynomials, hyperbolic functions and autoregressive series have been used (Misra, 1980). Among them, logistic curve has found support more than any other function on empirical grounds as well as the logic that the “population increase is proportional to the absolute population size already attained and the amount still left until the maximum, where the population becomes stationary” (UN, 1973).

LOGISTIC MODEL

Among all the growth models existing in literature, logistic model is most widely used model of population growth. The model and its assumptions are discussed below.