Psychologist Nina Strohminger at the University of Pennsylvania, who was not involved in the study, says she wants the effect to be real but cannot rule out some unknown confounding variable.

没有参与这项研究的宾夕法尼亚大学心理学家尼娜·施特罗明格指出，她希望这种影响是真实的，但不能排除一些未知的混杂变量。

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As far as skulls are concerned, there is one confounding variable: climate.

至于说到头骨，这里有个容易混淆的变化因素：气候。

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If that confounding variable can be taken care of, though, and the effect persists, the next obvious step is to determine what mechanism within the mother's body causes the discrepancy.

假设在排除这些变量因素的条件下(如果这些变量真的存在)，上述结果仍然生效，那么下一步就需要研究到底是母亲身体里的什么机制决定了子女的性别差异。

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It may be a confounding variable in studies of air pollution or other causes of disease.

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If that confounding variable can be taken care of, though, and the effect persists, the next obvious step is to determine what mechanism within the mother's body causes the discrepancy.

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We have to recognize that studies that carefully assess the effects of an exposure on health are extremely difficult to carry out correctly without the errors of bias and confounding and, thus, are of variable reliability and validity.

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