Sex Partners: Exploring Growth, Change and Impact Across Development

The number of sexual partners a person accumulates across their sexual history has been utilized as a marker of sexual health risk and adverse outcome risk. Yet, little is known about how individuals develop a sexual partner history, including critical times of change when individuals tend to gain more or fewer partners, and how individual factors impact growth in partners. Even less is known about how patterns of sexual partner growth impact adjustment and substance use outcomes. The current study utilized 8 waves of data, starting in the 10th grade, from 200 individuals (100 males, 100 females). This study explored trajectories of growth of partners from adolescence to young adulthood. First, longitudinal growth curve models were tested for best fit to the data, including linear, latent, quadratic, and spline models. Ultimately, a spline model with 3 slopes provided the best fit. The modeled slopes were from 10th grade (M age 15.9) to the end of high school (M age 17.9), from the end of high school to the year after high school (M age 19.4), and from the year after high school to the end of the study (M age 25.7). Next, I explored potential factors impacting sexual partner history patterns. These factors included timing of sexual debut, gender, religiosity, and verbal IQ. Timing of sexual debut, religiosity, and verbal IQ separately impacted rates of change of the accumulation of sexual partners. Gender was not associated with partner history growth. When all factors were considered together, sexual debut emerged as the most consistent predictor of partner history intercepts and slopes across adolescent and young adult development. Finally, the 3-spline model was used to measure associations among partner growth parameters and internalizing and externalizing symptoms and substance use. Externalizing symptoms and substance use were predicted by patterns of partner growth, and in turn predicted patterns of growth. Internalizing symptoms predicted levels of partners at the 10th grade only. Investigating questions such as those posed by the present studies could benefit intervention work, public health outcomes, and our understanding of the use of nonlinear models in examining complex patterns of behavior