The Census reports a 72 percent increase in the number of cohabiting couples since 1990. For many people in our culture, living together before marriage has been compared to taking a car for a test drive. The "trial period" gives people a chance to discover whether they are compatible. After all, the argument goes, you wouldn't buy a car before taking it for a test drive?

Yet here's the implication of the "test drive" metaphor: I am going to drive you around the block a few times, withholding judgment and commitment until I have satisfied myself about you. Pay no attention to my indecision, or my periodic evaluations of your performance. Try to act as if we were married, so I can get a clear picture of what you're likely to be like as a spouse.

Unfortunately, research shows that this test drive approach isn't just an equal alternative to marriage. Cohabiting couples report lower levels of satisfaction in the relationship than married couples. Studies have shown that cohabitation is correlated with unhappiness and domestic violence. And if a cohabiting couple ultimately marries, they have a higher propensity to divorce.

So here's the problem with the car analogy: the car doesn't have hurt feelings if the driver dumps it back at the used car lot and decides not to buy it. The analogy works great if you picture yourself as the driver. It stinks if you picture yourself as the car.