Dollars and Sex (30 page)

A more reliable measure of infidelity is the share of men who have children whom they mistakenly believe are their own, when they are, in fact, not related. Evolutionary biologist David Buss reports that in blind paternity studies, approximately 10 percent of children fall into this category. But this measures only female infidelity, and in an era in which approximately 40 percent of births are to unmarried women, even this fails as a measure of extramarital infidelity.

Bruce Elmslie and Edinaldo Tebaldi find that among Americans who are still married to their first husbands or wives, 7 percent of women and 14 percent of men said yes in response to the question “Have you ever had sex with someone other than your husband or wife while you were married?” When they consider only men and women under the age of 35, men and women appear to cheat at similar rates, with 7 percent
of women and 9 percent of men admitting to extramarital sex. As we will see, this difference between age groups probably stems from the timing of infidelity rather than a societal shift that has caused a new generation of men to cheat less and a new generation of women to cheat at roughly the same rate.

These numbers seem low and, the fact is, they underestimate the pervasiveness of infidelity because they represent only the behavior of people who are still in their first marriage—anyone ever divorced was excluded from the data set. Donald Cox, using data from a nationally representative survey, finds that people who report that they have cheated on a marriage partner at some point in their lifetime are more likely to be divorced; 49 percent of male and 56 percent of female cheaters are divorced, compared with 29 percent of male and 31 percent of female non-cheaters. So removing divorced people from the data set means that the propensity to cheat in marriage will be predicted as lower than it really is in the general population.

Donald Cox finds that 25 percent of men and 14 percent of women have had an extramarital affair at some point in their lifetime. If we ask only about behavior in the previous twelve months, 8 percent of men admit to having an extramarital affair compared with 3.5 percent of women. When we include people who are cohabitating, as well as those who are married, the share admitting to infidelity increases to 34 percent for men and 23 percent for women. We also know that men who cheat on their partner cheat more frequently than women do; cheating men are twice as likely as cheating women to have had sex with two or more partners in the past year. Men tend to cheat with women who are younger (no big surprise there) and women tend to cheat with men who are better educated. Very young women (less than 26 years old) cheat more than women of any other age, and while men also cheat more when they are young, the relationship between age and infidelity isn't nearly as pronounced for men as it is for women.

You might be wondering how thinking about infidelity from an economic perspective helps our understanding of this behavior. There's no
doubt that biology plays a huge role in encouraging married people to seek sex outside of their marriages, but, at some level, the final decision to act on those biological impulses is made by rational people seeking to maximize their well-being. As we will see later, that decision might not always make them happy, but nonetheless the decision to cheat is the optimal one at the time that it is made.

Let me introduce the economic model that can be used to explain infidelity. It will look familiar to you because it is the same approach we used in
chapter 1
. Rather than explaining how sexuality has changed over time, however, we will use it to explain why it is that some men and women are unfaithful while others are not.

UNFAITHFUL MATH

Men and women cheat in marriage because they believe at the outset that the benefit of doing so outweighs the expected costs. The expected cost of cheating looks something like this:

The probability of being caught cheating depends on an individual's circumstances. For example, consider two women who are both considering having an extramarital affair. The first woman works outside of her home, is financially independent, and lives in an urban environment. The second is not employed on the labor force, is financially dependent, and lives in a rural community. Without knowing any more information, it is reasonable to assume that the woman who works at home, and lives in a remote area, has a much higher chance of being caught cheating than the woman who works outside of the home and might even have opportunities to travel for business.

The “cost of being caught” is a little more complicated, but it too is an expected cost—no man or woman really knows what the cost of cheating is until they are caught. If neither the career woman nor the homemaker
is paid alimony in the event that her husband divorces her for adultery, the financially dependent woman has far more to lose by being caught cheating. If alimony is paid despite the infidelity, on the other hand, the dependent woman is more likely to be the recipient of alimony payments, and it is the financially independent woman who has more to lose. In fact, she might end up being the alimony payer if her husband earns a lower income.

The final thing we need to know is the probability that each woman's husband will leave if he catches her cheating. In reality we have no idea what those probabilities are as they will vary from woman to woman and from husband to husband. The husband of the financially independent woman might stay if he enjoys the financial stability their marriage gives him, or he might prefer financial insecurity to living with an unfaithful wife. The husband of the homemaker might leave if he is unwilling to support an unfaithful wife or might stay if they have young children whom he wants to protect.

We may not know what these probabilities are, but my guess is that these women already have a pretty good idea what will happen if their husband finds out they have been unfaithful before they make the decision to stray.

Let's say, for argument's sake, that the chance of the homemaker being caught cheating is 30 percent, the probability that her husband will leave her if she is caught is 50 percent, and, in the case of divorce, she loses $100,000 worth of goods and services that her marriage provided her. Her expected cost of cheating is then:

0.30 x 0.50 x $100,000 = $15,000

So the benefit of the extramarital sex would have to be large in order for her to cheat; she would have to value it more than $15,000 in monetary terms.

Now the woman who works outside of the home faces very different risks and costs. Let's say her chance of being caught cheating is only
5 percent, the probability that her husband leaves her if she is caught is 50 percent, and, in the case of divorce, she loses $50,000 worth of goods and services that her marriage provided her. Her expected cost of cheating is:

0.05 x 0.50 x $50,000 = $1,250

So the benefit of the extramarital sex is significantly lower for her than for the other woman. She would have to value it as more than $1,250 in monetary terms in order for her to cheat.

Anything that increases the chance a cheater will be caught (for example, if the likelihood of contracting an STD is high) or increases the chance that the partner will divorce him/her (for example, if he/she credibly commits to leaving) increases the expected cost of cheating.

Obviously, financial losses are only a convenient way to explain the costs in this analysis. Other considerations, those harder to measure, are also costs associated with being caught cheating. For example, cheating men and women risk the emotional cost of losing their children and, even if they don't lose their children, imposing hardship on those children in the case of divorce. Many cheaters, both men and women, risk retaliation for their infidelity in the form of physical violence from their partners. They risk losing their spouse's love for them, which is something most married people value. They risk being expelled from their faith communities or being socially isolated by family and friends. Others risk damaging their careers, particularly if the affair is with a colleague or client. Even the risk of living alone for an undetermined period imposes an expected cost on someone contemplating infidelity.

All of these factors, and probably many others, enter into the cost side of this infidelity cost-benefit analysis.

In the years that follow an extramarital relationship, a cheater may not feel that the decision to cheat was as rational as I have portrayed it to be here, especially if the expected costs have become real costs (for example, if the spouse both discovered their infidelity and asked for a divorce), but even decisions we later regret, in fact even the worst decisions you have made in your life, can be a rational decision at the time that they were made.