Illegal Drug Use, Depressive Symptoms, and General Health: Exploring Co-occurrence across 11 Years in a National Sample.

The co-occurrence of illegal drug use, symptoms of depression, and a lower perception of general health among adolescents continues to be of substantive interest for researchers and the general public alike. Research on this topic, however, remains relatively stagnant, focusing on narrow developmental periods and each association independently, with limited consideration for the existence of a nexus between the three constructs as individuals age. Considering these limitations, the current study examines the longitudinal progression, from adolescence to early adulthood, of illegal drug use, symptoms of depression, and a lower perception of general health. The National Longitudinal Survey of Youth 1997 (NLSY97; N = 8,984), measures over an eleven-year data collection period, and between-and within-individual analytical strategies were used to evaluate the nexus between the constructs. The findings suggested that illegal drug use, depressive symptoms, and general health at previous time periods directly and indirectly predicted illegal drug use, depressive symptoms, and general health at subsequent time periods. Moreover, the within-individual change in illegal drug use was associated with the change in depressive symptoms, and the change in depressive symptoms was associated with the change in general health. Practitioners should consider this co-occurrence when treating symptoms related to illegal drug use, symptoms of depression, and physical health.

Heteropaternal Siblings Misclassified as Dizygotic Twins: A Potential Biasing Factor for Heritability Estimates?

Heteropaternal superfecundation (HP) occurs when two or more ova are fertilized by sperm from separate males. The resulting siblings are genetically equivalent to half-siblings and share, on average, 25% of their inherited genetic material. In the absence of genetic testing HP siblings could be treated as dizygotic (DZ) twins in behavioral genetic analyses and bias heritability estimates in phenotypic decomposition models. However, the extent to which such misclassification could affect calculated estimates of heritability is currently unknown. Employing simulation analyses, the current study assessed the potential biasing impact across a variety of conditions varying by proportions of DZ twins, sample sizes, and low, moderate, and high levels of genetic and environmental contribution to phenotypic variance. Overall, the results indicated that misclassified HP siblings had minimal impact on estimates of heritability. Nonetheless, greater attention should be paid to the identification of HP siblings within existing and future twin datasets.