Research on long-term couples has long shown that differences in sexual desire are common, and there is no universal amount of sex that works for everyone. People use very different strategies to manage their own desire and negotiate with a partner.
There is also an important difference between sex someone wants and sex someone has in order to maintain a required frequency. The same number — “twice a week” — can describe completely different relationships: in one, both people look forward to those encounters; in another, one repeatedly agrees in order to avoid conflict.
So a single number tells us nothing about desire, the quality of the sex, or whether the partners’ needs actually match.
Statistics are useful when we want to understand how large groups of people live. They are much less useful as a ruler a couple uses every Sunday to measure whether their week was sexual enough.
Sometimes the best indicator of a sex life is not how many encounters happened, but how well the sex life that exists actually suits the two people living it.