The Demographic Discontinuity of the 1940s

Keyfitz, N. (1987). The Demographic Discontinuity of the 1940s. IIASA Working Paper. IIASA, Laxenburg, Austria: WP-87-092

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Abstract

The expansion of world population in the 20th century did not take place as a smooth acceleration, but showed sudden changes in the demographic parameters on at least two occasions. The main one was in the 1940s. when the amount of increase between cohorts rose three fold within as little as five years; an earlier similar increase took place about 1920. Earlier than these, a rise about the year 1900 is suggested. All of this is inferred from censuses taken since 1950. Nothing beyond data on age distributions at five year intervals from 1950 onwards is needed to estimate intercohort increases with small and measurable error. A check on the process is to proceed backwards, and apply the calculated average intercohort increases to reconstruct the original age distributions. Intercohort increase is a net amount that includes some decrease of mortality, especially infant mortality, and some increase of fertility.

The technique used provides new information concerning the onset of the so-called population explosion. For the world as a whole that onset was especially sudden because of the coincidence of the postwar baby boom in developed countries and the fall in mortality due to inoculation and antibiotics in the less developed. The measure of discontinuity being linear and additive. it can be decomposed precisely by continents and countries. Besides the MDCs, the mid 1940s showed a leap forward in Malaysia, Egypt and Turkey; the corresponding leap took place about five years later in Pakistan, Vietnam and Indonesia. China accelerated over a longer period, something like 10 years rather than 5. The acceleration occurred also in Latin America but there it started earlier and continued longer and more slowly. Tropical Africa shows little discontinuity in the rate of change, but very rapid growth throughout, perhaps due to shortcomings of the data.

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