Resumen

Este estudio explore la relación de sexos humanos al nacimiento para cuatro variables seleccionadas: Año calendario, color, edad de la madre y paridad de la madre. En el análisis de variancia la relacion de sexos al nacimiento se ha encontrado que difiere significativamente por color, edad de la madre y orden de nacimiento del chico. Ningun efecto de la interacci6n entre esas variables se ha encontrado que sea significativo, y adicionales analisis de la fecha de nacimiento indican que ningun efecto generalizado de la edad de la madre sobre la relación de sexos puede ser definido.

La relacion de sexos de los nacimientos de blancos se ha encontrado que es consistentemente mas alta que la de los de no blencoe, este hallazgo es consistente con anteriores estudios. Parte de las diferencias por raza quizas pueda ser explicada por diferencias en ambientes socioeconómicos. Por el momento la diferenie relación de sexos para bloncos y no blancos señala la necesidad de realizar más exploraciones de causalidas entre diferentes modelos de fertilidad.

Ademas el análisis de variancia indica una relacion inversa de la relacion de sexos de acuerdo a la edad de la madre. De hecho, la inclinacion descendente de la relación de sexos se hace empinada cuando avanza la edad de la madre. Las regresionesson curvas porque las comparaciones parabolicas son significantes.

Finalmente, el orden de nacimiento de los chicos esta inversamente asociado con la relación de sexos al nacimiento. Ademas, cuanto mayor es la proporción de chicos primogenitos, más alta sera la total relación de sexos. Este hallazgo es consistente con estudios previos que han mostrado que el orden de nacimiento tiene un efecto definido sobre la relacion de sexos al nacimiento, independientemenie de la edad de la madre.

Summary

This study explores the relation of the human sex ratio at birth to four selected variables: calendar-year, color, maternal age, and parity of mother. In the analysis of variance, the sex ratio at birth is found to differ significantly by color, age of mother, and birth order of child. No effect of the interaction among these variables is found to be significant, however, and further analyses of the birth data indicate that no generalized effect of the age of mother on the sex ratio can be drawn.

The sex ratio of white births was consistently higher than that for nonwhite births—a finding which is consistent with earlier studies. Part of the racial differences can perhaps be explained by differences in socioeconomic environment. For the moment, the differential white-nonwhite sex ratio points to further exploration of causality between different patterns of fertility.

Further, the analysis of variance indicated an inverse relation of sex ratios to maternal age. In fact, the downward slopes of the sex ratios become steeper with advancing age of mother. The regressions are curved because the parabolic comparisons are significant.

Finally, the order of birth of children is found to be inversely associated with the sex ratio at birth. Moreover, the higher the proportion of first-born children in a given year, the higher were the verall sex ratios. This finding is consistent with previous studies that have shown that birth order ohas a definite effect on the sex ratio at birth, regardless of the age of the mother.

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