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Factors affecting the sex ratio in large populations

Published online by Cambridge University Press:  27 September 2011

Michael S. Teitelbaum
Affiliation:
Nuffield College, Oxford, and Epidemiology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland

Summary and conclusions

To summarize the findings presented here, only three of the five factors studied appear to be independently related to the sex ratio at birth. The significant negative birth-order effect, which in the first analysis accounted for a 2·6% shift in the relative odds of male birth, remained significant when adjustment for the race effect was provided in the second analysis. The magnitude of the effect was diminished by this adjustment, however, indicating that analysis for birth-order effects in the absence of adjustment for the race factor may lead to over-estimates of the importance of the birth-order factor.

The significant race effect detected in the second analysis resulted in a 3% lower relative odds for a Negro male birth than that for a white. This racial difference, coupled with the non-uniform distribution of Negro births by paternal-age and birth-order categories, appears to be the source of the mysterious ‘interactioneffect’ between birth order and paternal age reported by Novitski & Kimball. The race effect remained significant after adjustment was provided for both the birthorder and socio-economic effects.

Type
Sex ratios in different populations
Copyright
Copyright © Cambridge University Press 1970

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