Since you like "statistical tricks," here's another one for you. Couples who practice natural family planning, rather than using artificially induced sterility, enjoy a divorce rate of less than 5%. (Marital duration and natural family planning)
So basically, this "statistical trick" proves that couples who do not live together before marriage, and who joyfully welcome children into life, walmost never divorce.
This "statistical trick" used to be called common sense.
No, its merely a reflection of the fact that couples that are willing to exert this level of discipline are the type that are predisposed to put the work into a marriage. Virtuous behavior before a marriage is a characteristic of those that are likely to succeed at marriage, not a cause of the successful marriage.
Put another way, compelling a loser to put on a suit and tie and get to the interview early does not mean that he's going to put in eight hours a day, forty a week, after he gets the job.