A Theory of Marital Sexual Life

Why does the frequency of marital sex decrease with marital duration? Does the probability of involvement in extramarital sex increase or decrease with marital duration, and why? I develop a theory to answer these questions. I apply the law of diminishing marginal utility and human capital theory to explain the basic observed decline in the frequency of marital sex with marital duration. Based on the above explanation, I develop a discussion on the relationship between marital duration and extramarital sex, and I derive two hypotheses, which are supported by statistical analyses of the National Health and Social Life Survey data.