Strategies for combining and scaling sexual maturity indicators: the Heartfelt Study

Primary objective: To identify the best variable or combination of sexual maturity variables to use in investigations of adolescent health, and explore possible re-scaling of five-stage sexual maturity stages into 'dummy variables' ('advanced'/'delayed'). Research design: Cross-sectional. Subjects: Tri-ethnic sample of 384 US adolescents 11-16 years of age (Heartfelt Study). Methods: Sexual maturity variables are genital, breast and pubic hair stages obtained by clinical examination by nurse practitioners, testes size, menarche and age at menarche. Results: Principal factor analysis of sexual maturity variables, height and age, revealed high commonality among the variables, as no more than a single factor appeared in 27 of 28 factor analyses (by sex and age groups). Genital singe (boys) and breast stage (girls) were most highly related to the first principal factor independent of age and ethnicity. ANOVA of 'key variables' indirectly reflecting endocrine function suggested that some stages could be combined. Conclusions: A single variable should suffice to describe sexual maturity at the studied ages, or variables could be combined in a (unstandardized) sexual maturity index (SMI): SMI (Girls) = 0.998 x BREAST + 0.900 x PUBIC HAIR + 1.815 x YEARS SINCE MENARCHE, SMI (Boys)= 1.104 x GENITAL + 1.328 x PUBIC HAIR + 5.997 x TESTES SIZE (mL), There is modest support for re-scaling a sexual maturity variable into 'delayed' and 'advanced' groups if needed, thus: (stages 1, 2, 3, vs 4, 5).