'Mostly Catholic' colleges have higher rates of sexual 'hookups' than other less religious campuses in the US, the author of new research has revealed.

Jason King, professor of theology at Saint Vincent College in Pennsylvania, has said he is 'astounded' by the dominance of a 'hookup culture' across college campuses.

King, who defines hookups as a 'sexual interaction with no expectation of a subsequent relationship', said students think 'there's just no viable alternative' in an interview with the Newman Society.

'It stuns me that everyone assumes either you hook up or you're totally out of the social world. Even on very Catholic campuses where by far most people do not hook up... students still felt like they have to wrestle with [the hookup culture] and explain their rejection of hooking up, even though it wasn't on their campus,' he said.

He graded Catholic colleges as either 'very Catholic', 'mostly Catholic' or 'somewhat Catholic' according to religious adherence among pupils and the level of enforced religious practices such as Mass and co-ed residence halls.

'I expected a simple scale – the more Catholic a college was, the less hooking up there would be – a linear relationship,'

But instead, while 'very Catholic' colleges had the lowest rates of hooking up at less than 30 per cent, the highest rate is on 'mostly Catholic' campuses where 55 per cent of students hook up.

This was compared to less than half of students (45 per cent) at colleges that were just somewhat Catholic.

King said at very Catholic colleges religious devotion was higher than others, leading to the lower levels of hookups. But he said the reason there wasn't a linear progression was because many students at somewhat Catholic colleges come from disadvantaged backgrounds and focus on getting a degree.

'They see hooking up as too risky, jeopardizing their education and their future, King writes in First Things.