I'm with Sarah_H i thought it would be 50/50. All I know is that the male sperm swims faster and the female sperm lives longer. So if you want a boy you would have to have sex right on ovulation as male sperm would reach there first, however to have a girl you would have to have sex either side of ovulation as they live longer than male sperm and would still be there when you O'd.

I'm pretty sure this is right. Anyway all the best.

Love