It's not zero extra effort. If you want to maintain your statistical power for both male and female, that means doubling your sample size. And it's unlikely tha

It's not zero extra effort. If you want to maintain your statistical power for both male and female, that means doubling your sample size. And it's unlikely that they'll be identical 99.9% of the time. The article suggests that we'd see frequent, small differences, but there haven't been enough studies of this type to know for certain.