That’s a pretty strong effect:

The research found that 42 percent of students in coed housing reported binge drinking on a weekly basis, while only 18 percent of those in single-sex housing did so. The researchers discounted the idea that student self-selection may result in those likely to engage in binge drinking opting to live in mixed-sex housing. Their rationale is that most students living in single-sex housing didn’t request to do so, but were placed there by campus officials when coed slots are filled.