The contact hypothesis postulates that being near people of a different social group (e.g., race, class, sexual orientation, etc) translates into greater tolerance for that type of person. In other words, it’s harder to hate all Latinos (for example) when your neighbor is Latino and, damn it, you kind of like him. Andrew Sullivan posted this figure:
Jose at Thick Culture suggests that this could be evidence for the contact hypothesis. But he also asks whether it might also be true that less homophobic people are more likely to come into contact with gays and lesbians because of a third variable that correlates with both (like choosing to live in a big city), making the relationship spurious.
(What’s a spurious relationship? Here’s one: People who eat ice cream are more likely to drown. Both incidence of ice cream eating and rates of drowning are related to summertime. The relationship between ice cream and drowning is spurious. That is, there is no relationship. Yet they appear related because they are both related to a third variable.)