Marriage does not bring stability to a relationship

I've posted here before about the logical error in David Cameron's claim that marriage makes relationships more likely to last. A study by the Institute for Fiscal Studies has found that although cohabiting couples are more likely to split up than married couples, this does not prove cause and effect. Cohabiting couples who split up by the time their child is five are typically younger, poorer, and less likely to plan their pregnancies. When these differences are allowed for the two groups have almost the same incidence of break-up.

In advocating marriage as a preventive for family break-up Cameon is falling into the familiar trap of mistaking association for causation.