Economic stress affects the human sex ratio: A retest of the Trivers–Willard hypothesis in Poland
Economic stress affects the human sex ratio: A retest of the Trivers–Willard hypothesis in Poland

Summary/Abstract: This paper contributes to the verification of the Trivers–Willard hypothesis (TWH). Based on theTWH, observed sex (male-to-female) ratio at birth in a population is presumed to decline when parentsexperience economic stress. The empirical evidence so far is mixed.The research material consisted of data on the total numbers of live male and female births in thePolish population in the years 1995–2020. The data were used to produce semiannual time series forsecondary sex ratio (SSR), and the sex ratio at birth (SRB). The variable describing the economic stress ofhouseholds was percentage change in private consumption. The statistical method proposed by Catalanoand Bruckner – expanded to include additional statistical analyses – was applied to retest the economicstress hypothesis. The analysis led to complementary ARMAX models, explaining SSR or SRB variancebased on autoregression and the moving average process, as well as private consumption. The resultsindicate that periods of decreasing consumption favored mothers having daughters, while periods ofincreasing consumption favored mothers having sons. The number of “additional” male births resultingfrom improved economic conditions was calculated for the period of study. Consequently, the economicfactor was shown to have a positive effect on the human sex ratio. At the same time, it should be notedthat SSR and SRB reaction lags to consumption changes were different for Łódzkie Province (one year) andfor Poland (two years).The obtained results led to the “correct” verification of the Trivers–Willard hypothesis (TWH):economic stress affected the SSR and SRB in Poland. Both SSR and SRB were useful in analyzing economicstress (a dual solution). The use of a greater density of data points was shown to improve analysis effectsand increase the likelihood of a “positive” verification of the economic stress hypothesis.

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