Indeed, the guilty secret of psychology and of behavioral economics is that their experiments and surveys are conducted almost entirely with people from Western, industrialized countries, mostly of college age, and very often students of psychology at colleges in the United States.

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Dr Jacky Boivin, from the School of Psychology at Cardiff University, studied 71 women with an average age of 30.

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When men outnumber women, females marry younger and the age gap between spouses grows, the study, published in the journal Evolutionary Psychology, says.

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