This proposed R03 project focuses on an understudied but important question: how is hormonal contraceptive method use associated with the frequency of sexual intercourse among mixed-sex couples? Hormonal contraception is a safe and effective way to avoid undesired pregnancy, and 80% of sexually active women have used the oral contraception pill (Guttmacher 2020). However, some evidence suggests that sexual side effects of hormonal contraception – including decreased arousal and sexual functioning – may lead some couples to discontinue its use (Higgins & Smith 2016; Sanders et al. 2018), leaving them vulnerable to an undesired pregnancy. Very little research has described the links between hormonal contraceptive use and sexual intercourse, and the studies that have explored these links have been undermined by cross-sectional designs, small samples, and/or neglect of the intimate relationship context. We propose a state-of-the art statistical analysis of existing intensive longitudinal survey data. The survey data are from 953 young women (ages 18-22) who participated in an NICHD-funded project, the Relationship Dynamics and Social Life (RDSL) study, which collected weekly surveys on intimate relationships, mixed-sex sexual intercourse, contraceptive use, and pregnancy for 2.5 years beginning at age 18 or 19. This data—with repeated surveys within each relationship—provides the first opportunity to describe the interconnections between heterosexual intercourse and hormonal contraceptive use across the course of these relationships. We have three specific aims for this project. First, we will estimate logistic regression models of the weekly probability of sexual intercourse, using a within-between fixed-effects/random-effects (hybrid) specification, to test our hypothesis that a mixed-sex couple’s probability of having sexual intercourse is lower when they are using a hormonal contraceptive method than when that same couple is not using a hormonal method. Second, we will use the same methods to test our hypothesis that the consequences of hormonal contraceptive use for sexual frequency will accumulate over time, net of relationship duration. Third, we will use multilevel (mixed effects) models, which easily permit the inclusion of cross-level interactions between upper-level (individual/relationship) characteristics and hormonal contraceptive use as predictors of sexual frequency, to test our hypothesis that the association between hormonal contraceptive use and sexual frequency differs depending on the characteristics of the intimate relationship. We propose a complementary, uniquely qualified investigator team: Dr. Jennifer Barber, Professor of Sociology and Senior Scientist at the Kinsey Institute (PI of RDSL project; expert in intimate relationships and contraceptive use) and Dr. Shari Blumenstock, a post-doctoral fellow at the Kinsey Institute (expert in sexual behavior and intimate relationships).