The formula explained

L = 8 + .5Y - .2P + .9Hm + .3Mf + J - .3G - .5(Sm - Sf)2 + I + 1.5C

L: The predicted length in years of the relationship

Y: The number of years the two people knew each other before the relationship became serious

P: The number of previous partners of both people added together

Hm: The importance the male partner attaches to honesty in the relationship

Mf: The importance the female attaches to money in the relationship

J: The importance both attach to humour (added together)

G: The importance both attach to good looks (added together)

Sm and Sf : The importance male and female attach to sex

I : The importance attached to having good in-laws (added together)

C: The importance attached to children in the relationship (added together)

All measures can be scaled from 1 to 5 where 1 is not important at all and 5 is very important.

Research findings for same sex couples differed slightly with the formula being adjusted to L = 8 + .5Y - .2P + 2J - .3G - .5(S1 - S2)2 - I + 1.5C (where S1 and S2 are the two partners' ratings for the importance of sex).