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Wednesday, November 30, 2005

Bo Malmberg and The Four Phases of the Demographic Transition

The Swedish demographer Bo Malmberg has offered us a four-phase typology of the demographic transition which is not without interest.

Clearly the impact of the demographic transition on population size and growth rates has been considerable over the last couple of centuries, and it is probably this aspect more than any other that has attracted all the popular attention. Less well appreciated and less well publicised, however, has been the fact that the impact of the transition on the age structure of populations has been an equally strong and significant one.

Further, impacts on age structure tend to be more extended in time. Indeed as I am arguing here, the demographic transition may in fact best be thought of as an extended and continuous process of age-transition. Now, according to Malmberg this age transition consists of four distinct phases, each of them marked by the strong specific weight of one age group. The onset of the transition (which is characterised by a sharp decline in mortality) creates a child phase, then, as fertility begins its decline comes a young-adult one, acceleration of the fertility decline towards replacement fertility produces a phase of population maturity, or adult stage, and finally sustained below-replacement fertility produces in its wake an elderly society.

The first phase of the age transition, the child phase, occurs when falling death rates produce an increase in the number of children. The reason for this increase is fairly self explanatory in that in earlier high-mortality populations, most of those who die are infants and children. Added to this, the process of cohort maturation means that the increasing numbers surviving into adulthood produce yet more children and so on, since the available fertile population grows continuosly, and, with unchanged fertility behaviour, this will inevitably further increase the number of children born.

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