When it comes to keeping marriage vows, women may be better at the "in sickness and in health" part than men.

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For example, if a wife is diagnosed with a serious disease, there's a 6 percent higher chance of divorce compared to healthy couples, according to a new study from Iowa State University. But there is no change in the probability of divorce when it is the husband who is diagnosed with an illness. The study focused on people 51 and older who were diagnosed with at least one of four serious illnesses — heart disease, stroke, cancer and lung disease.

Researchers conjectured the main reason for the discrepancy is that older men are less comfortable than women in the role of being a caregiver.