Changes in Income at Macro Level Predict Sex Ratio at Birth in OECD Countries

The human sex ratio at birth (SRB) is approximately 107 boys for every 100 girls. SRB was rising until the World War II and has been declining slightly after the 1950s in several industrial countries. Recent studies have shown that SRB varies according to exposure to disasters and socioeconomic conditions. However, it remains unknown whether changes in SRB can be explained by observable macro-level socioeconomic variables across multiple years and countries. Here we show that changes in disposable income at the macro level positively predict SRB in OECD countries. A one standard deviation increase in the change of disposable income is associated with an increase of 1.03 male births per 1000 female births. The relationship is possibly nonlinear and driven by extreme changes. The association varies from country to country being particular strong in Estonia. This is the first evidence to show that economic and social conditions are connected to SRB across countries at the macro level. This calls for further research on the effects of societal conditions on general characteristics at birth.人类出生性别比（human sex ratio at birth, SRB）通常约为每100名女婴对应107名男婴。出生性别比在第二次世界大战前持续攀升，1950年代后，多个工业化国家的该指标已出现小幅回落。近期研究表明，出生性别比会随灾害暴露情况与社会经济条件的变化而出现波动。但目前仍未明确，能否通过可观测的宏观层面社会经济变量，解释多年间多国的出生性别比变化情况。本研究显示，宏观层面可支配收入的变化正向预测经合组织（OECD）国家的出生性别比：可支配收入的变化每增加1个标准差，每1000名女婴对应的男婴出生数量便会增加1.03例。该关联可能呈非线性特征，且由极端变化所驱动。各国间的关联程度存在差异，在爱沙尼亚尤为显著。这是首项证明宏观层面经济与社会条件与多国出生性别比存在关联的研究证据。该发现呼吁学界开展更多关于社会整体状况对人类出生时一般特征影响的相关研究。