In the Sabinas and Poznan populations, BMI shows only modest sexual difference, yet Progreso has many girls much heavier than expected. During maturation, Poznan girls are a little thinner than the boys, whereas in Sabinas the opposite occurs and recurs in Ramón's (1976) sample of Mexico City elite students. Progreso students, especially the girls, are more stocky than the others. Ramón found that some Mexico City girls reached 22 BMI at 15 and boys at 17 years.