One in five has tried an open arrangement

Two nationally representative US samples totalling around 8,700 adults were asked whether they had ever been in a consensually non-monogamous relationship — open, swinging, polyamorous, or otherwise agreed. Twenty-one per cent said yes. The figure held steady across gender, race, education, income, religion and political affiliation.

Swinging in the narrow sense — couples exchanging partners socially — is a much smaller slice, generally estimated between two and four per cent of adults. The gap between the two numbers is the point: most people who have tried something open did not do it in a club.