Essay Title: 

Demographic Transition in Asia and elsewhere

March 27, 2016 | Author: | Posted in ecology, nature

Demographic Transition in Asia and elsewhere

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The tracing of fertility trends by traditional measures in the early stages of a demographic transition is speculative and uncertain even if the data are of good quality . Alterations in exposure to risk through fluctuations in the intensity and patterns of mating are hard to allow for with sufficient accuracy . When the data are subject to significant reporting errors (even when quite modest , as in most Third World countries , the difficulties are [banner_entry_middle]

exaggerated greatly . It is no surprise then that there is a history of controversy about the nature and indeed existence of fertility falls in many countries . Mexico and Brazil in the 1970s , Pakistan in the 1980s , and Nigeria and Senegal currently are notable examples Much of the confusion and uncertainty can be avoided by analyses using parity progression ratios . These are the proportions of women who proceed from a birth of n to the next of n 1 over their lifetime (Brass 1989 . The simplest and most intuitively obvious measures are for cohorts of women born in the same years or initiating family building in the same years , but synthetic time-period analogues have also been defined Parity progression ratios for a cohort of women are simply a reorganization of the distribution of completed family sizes at the end of the reproductive period . Unlike the traditional rates , these indices are not affected by the timing of births in the family build-up and hence by the transient effects of alterations in mating patterns . The parity progressions provide robust evidence on the trends in family size which are basic to long-term developments in fertility . Of course , the estimation of precise measures is dependent on accurate reporting of errors in the latter are particularly frequent in Third World surveys Series of parity progression ratios for cohorts have been exploited effectively to trace fertility trends . Two limitations are apparent both of which are a consequence of the need for family completion before the measures can be calculated . In the Third World , birth registration or notification is virtually nowhere good enough as a basis for the analyses . Reliance must be put on censuses and surveys where births to women are recorded . Unfortunately , it has been relatively rare for such histories to be collected for women over 50 years of age . The series of cohorts for which measures can be calculated are , therefore very short . They are also dominated by the fertility of some time in the past since the impact of recent trends on the completed family sizes is relatively small The approach has been extended to cohorts of incomplete fertility by the calculation of surrogate measures of parity progressions . By standard life table methods , the probabilities of movement from the nth to the (n 1 )th birth in time intervals can be computed , and hence the proportions of women attaining the subsequent birth within different periods , provided that there are adequate observations… [banner_entry_footer]

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