The following is an excerpt from "The Secrets of Surviving Infidelity" and reprinted by permission of Scott Haltzman, MD and Johns Hopkins University Press

How frequent are affairs? It depends on how you define affairs, who you ask, and how they interpret the numbers. Among experts, there is no consensus on this issue. One of the most widely acknowledged statistics is this: about 1.5 percent of people will have an affair for each year of marriage. Not so bad, you might think. But that’s only per year. In other words, after ten years the rates go up to 15 percent, and after twenty years, 30 percent of married people have had an affair.

This statistic highlights a paradox. Most people assume that the longer a couple has been married, the greater the strength of the union. That’s supported by the data that show that an awful lot of spouses end their marriage within the first few years. But, the longer you’re married, the more time you have for things to happen: the more likely you are to win the lottery, get in a car accident, or see an albino deer munching on your vegetable garden. That’s why some researchers at the University of Chicago have come up with what appear to be puzzling findings. While they show pretty consistently that every year, 10 percent of spouses admit to cheating (12 percent of husbands, 7 percent of wives), people who are over the age of 60 actually have the highest rates of infidelity over a lifetime. For those of you who think of this population as the ones who populate the “Help I’ve Fallen and I Can’t Get Up” commercials, remember that, at the time of the study, 60-year-olds would have included Mick Jagger, Eric Clapton, Tina Turner, and Carly Simon. I’m not saying that any of these rock stars had affairs, but I am painting a picture for you of what life was like when people who are now sixty were coming of age. They lived in some wild times!

These data tell us that among the 60-plus crowd, 28 percent of all men and 15 percent of all women have had at least one affair. These studies don’t make clear which homes have had both husband and wife having affairs, and which homes were affected by only one person’s infidelity, so the total number of marriages that are affected ranges from 28 to 43 percent.

I did warn you that not all research is created equal. When Shere Hite, author of the Hite Report, published data on affairs, she concluded that 70 percent of American women who were married for more than five years had broken their marriage vows at least once. I know that sounds outrageous; even I think that’s out of bounds. But I recall a very unscientific discussion with one of my mentors from medical school, who maintained a very successful Park Avenue practice, and he claimed that every single one of his patients had had an affair at one time or another.

The take-home message from all this research is loud and clear. Affairs are not rare. Remember that exercise you did in your assemblies in high school (whether the subject was bullying, drug addiction, or STDs)? You know the one—where the speaker at the podium tells you to look to your right, then look to your left, and that either you or one of the people you are looking at will be affected by (fill in the blank with bullying, drug addiction, STDs, or whatever else the speaker is trying to convince you to avoid). Well, I’m that speaker. Look to the house on the left of you, look to the house on the right. Research tells us that your home or one of these other two homes will have someone who is affected by infidelity.

If that home is yours, it doesn’t mean you have to lose hope or lose face. The next chapters examine the causes of infidelity. Understanding “why?” is the first step toward finding ways to recover from its devastating effects.

The Secrets of Surviving Infidelity is available now.