Birth order compatibility

When it comes to birth order compatibility, studies suggest that opposites attract and the best birth-order mixes have the least of what Cane refers to as rank conflict: "Two firstborns, for example, have the same rank and would be expected to fight over who's the leader," says Cane. "Similarly two lastborns could be expected to experience conflict over who's to be considered the baby of the relationship."

So which marriage combinations work best? Dr. Kevin Leman, author of The Birth Order Connection, shares his findings:

Most compatible birth orders

Firstborn and lastborn / middle child and lastborn / only child and lastborn

This relationship works great, because the lastborn is going to be the fun-loving partner who teaches the other that it's okay to kick back and relax every now and then, while the firstborn/middle child/only child teaches his or her partner the importance of perseverance and why life should be taken seriously at times.

Least compatible birth orders

Firstborn and firstborn

When two bossy firstborns pair up, there is likely to be high friction. There could be plenty of conflict as both parties fight for control or they could fall into a controller-pleaser mode.

Lastborn and lastborn

Two adventurous individuals may mean double the fun and craziness at first, but with nobody to take charge, this relationship could turn chaotic very soon.

Only child and only child

Control issues aside, neither have much of a clue about the other gender.