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1 October 2008 Poisson Variations of the Sex Ratio at Birth in African Demographic Surveys
Michel Garenne
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Variations of the sex ratio at birth (SRB) were investigated using maternity history data collected in demographic surveys conducted in sub-Saharan Africa. Thirty-three countries were covered, totaling about 2.0 million births. The average SRB was 1.034 and varied by ethnicity, birth order, and maternal age. The effect of maternal age was significant for younger mothers (12–19 years old) and older mothers (40–49 years old), with a decline in sex ratios with increasing maternal age in both cases. The effect of birth order was significant only for the 20–39-year-old women, with a decline in sex ratio with increasing birth order. These two effects were similar for the three main population groups identified: populations from southern, eastern, and central Africa (SRB = 1.015), populations from West Africa and Sahelian countries (SRB = 1.040), and populations from Nigeria and Ethiopia (SRB = 1.087). In contrast, no effect of marital duration was found.

Michel Garenne "Poisson Variations of the Sex Ratio at Birth in African Demographic Surveys," Human Biology 80(5), 473-482, (1 October 2008).
Received: 20 April 2008; Accepted: 1 September 2008; Published: 1 October 2008
birth order
demographic and health surveys
marital duration
Poisson variation
secondary sex ratio
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