The Most Common Response: In a study of over 26,000 Americans, participants reported having sex 54 times a year, which averages out to approximately once a week. The sample included those who were single, dating, married, and cohabitating. When the authors looked at married couples specifically, the average sexual frequency was slightly lower, at 51 sexual encounters a year, or just less than once a week on average.
The Happiest Response: In a study of over 30,000 Americans, researchers examined the relationship between how often couples reported having sex and whether that related to their reported level of happiness. The researchers concluded that couples who were having sex once a week were the happiest, while couples who reported having sex 2, 3 (or more) times a week, were no happier than those having sex once a week.
The Potentially Problematic Response: The study described above, which focused on sexual frequency and happiness, did conclude that those who were having sex less than once a week reported lower levels of happiness than those having sex once a week (or more).