According to the National Opinion Research Center, the average American couple reports having sex 66 times a year. Married adults under age 30 say they have sex an average of 109 times a year. The average number drops to 70 times per year for 40-somethings and 52 times a year for people in their 50s.

Experts say women's sexual inclinations are more complicated than men's. While men are very rigid and specific about who they become aroused by, women have less-directed sex drives. Researchers say women are more likely to call themselves bisexual and that their sex drives overall are more “fluid” and can be more heavily influenced by social and cultural factors.

Erect, the average penis length is between 5 and 6 inches. When flaccid, penis size averages around 3.5 inches.

Only 10% of men reported a preference for oral sex to achieve orgasm, while 18% of women reported that preference. Men are more likely to reach orgasm when sex includes vaginal intercourse, but women are more likely to reach orgasm when they engage in a variety of sex acts that include vaginal intercourse or oral sex.

A study in the Journal of Sexual Medicine found that the average duration from the beginning of vaginal penetration until ejaculation was 5.4 minutes.

One more reason for men to avoid stress: It can make your penis shrink, if only temporarily. A man’s flaccid penis varies in size considerably because of various environmental factors and their effects on the sympathetic nervous system. Cold water and cold air are perhaps the best known causes of this “shrinkage” phenomenon, but psychological stress can do the same thing.

Women over 50 are more likely to report orgasm when a sexual event is with someone who is not a relationship partner. Researchers speculate that many newly divorced or widowed women may find the novelty of a new partner arousing.

Most masturbation is safe and healthy, sex therapists say. And it can improve sexual function and relationships by teaching both men and women about their own sexual responses, so they’re better able to explain to their partner what feels good to them. However, people who become too obsessed with solo sex can develop sexual problems or lose interest in sex with their partners. Finally, masturbation can, in fact, cause injury; frequent or overly vigorous masturbation can irritate the skin of the penis, and men who masturbate face-down can injure their urethras.

While the majority of adult men under 60 think about sex at least once a day, only about one-quarter of women report this level of frequency. As men and women age, each fantasize less, but men still fantasize about twice as often.

Among women who are part of a couple, 29% report that they always have an orgasm.

Among men who are part of a couple, 75% report that they always have an orgasm.

Most women require clitoral stimulation to reach orgasm. For women who have trouble achieving orgasm, incorporating clitoral stimulation into sexual activity may be all that is necessary.

Whether the G-spot exists is a matter of debate. Popularized by a 1982 book, the G-spot is a region found behind the pubic bone that has been credited as the trigger for a vaginal (vs. clitoral) orgasm, and even a catalyst for female ejaculation. However, some experts note that there’s no unique anatomical structure where the G-spot is supposed to be located. If the G-spot exists, it’s best described as an erogenous zone rather than a part of a woman’s anatomy.

While people with a history of stroke or heart disease should consult their doctors about sexual activity, for the most part, sex is a healthy form of exercise for older people. Researchers who tracked 914 men for 20 years found that having sex twice or more a week reduced the risk of fatal heart attack by half, compared with those who had sex less than once a month. They also found frequency of sex was not associated with stroke.