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. 1979 May;42(4):457-65.
doi: 10.1111/j.1469-1809.1979.tb00679.x.

The secondary sex ratio, paternal age, maternal age and birth order in Japan

Y Imaizumi, M Murata

The secondary sex ratio, paternal age, maternal age and birth order in Japan

Y Imaizumi et al. Ann Hum Genet. 1979 May.

Abstract

The simultaneous effects of several variables on the secondary sex ratio have been examined using data from over 3.7 million births which occurred in Japan during 1975--6. A weak and negative association between sex ratio and birth order was observed but it was not significant in the statistical sense. A negative effect of paternal age--birth order interaction was obtained when maternal age was controlled. The quadratic model is much more powerful than the linear model in explaining the sex ratio variability.

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