In that study which involved 19,065 people during a 15-year period, rates of infidelity among men were found to have risen from 20 to 28%, and rates for women, 5% to 15%.
A survey conducted in 1990 found 2.2% of married participants reported having more than one partner during the past year.
Studies suggest around 30–40% of unmarried relationships and 18–20% of marriages see at least one incident of sexual infidelity.
In one study, rates were higher in more recent marriages, compared with previous generations; men were found to be only "somewhat" more likely than women to engage in infidelity, with rates for both sexes becoming increasingly similar.
Another study found that the likelihood for women to be involved in infidelity reached a peak in the seventh year of their marriage and then declined afterwards; whereas for married men, the longer they were in relationships, the less likely they were to engage in infidelity, except for the eighteenth year of marriage, at which point the chance that men will engage in infidelity increases.
Differences in sexual infidelity as a function of gender have been commonly reported.
It is more common for men compared to women to engage in extradyadic relationships.
A study published in 2002 suggested there may be sex differences in jealousy.