Genetic analysis of behavioral differences among human beings requires both careful experimental design and appropriate genetic models. Any genetic study must be (1) valid and precise measures of individual differences, (2) appropriate methods to ascertain biological relationships, (3) research subjects who have been randomly recruited, (4) appropriate sample sizes, and (5) appropriate genetic models to interpret the data. In addition, the researchers must exercise caution in interpreting biosocial effects from the observed phenotypic correlations. To date, all studies of the genetic basis of sexual orientation of men and women have failed to meet one or more or any of the above criteria.