Time-varying effects of predictors of sexual risk

behavior in adolescents and young adults

Sara A. Vasilenko, Stephanie T. Lanza, Runze Li & Jennifer S. Barber

Outline

• Background on time-varying processes in sexual behavior

• Time-varying effect model (TVEM)• Examples

– Add Health– RDSL

• Summary and Implications

Background

• Meaning and riskiness of sexual behavior can vary over time– Adolescence v. Midlife– Time in a relationship

Background

• Traditional methods don’t account for these time-varying processes– Collapse across age, divide into groups– Changes occur in continuous time

TVEM

• Time-varying effect model (Tan et al., 2012; Shiyko et al., 2012)

• Flexible, nonparametric method for analyzing time-varying effects

• Versions for continuous, dichotomous, zero-inflated Poisson outcomes– Logistic TVEM (dichotomous) presented

• Macro available at methodology.psu.edu

Logistic TVEM

• where

TIME-VARYING PREDICTORS OF RISKY SEX OVER DEVELOPMENTAL TIME

Example 1

Sample Questions

• How do odds of having multiple partners change over time from early adolescence to young adulthood?

• How does the association between heavy episodic drinking and multiple partners change over time?

• How do these differ by gender?

Method

• Data from 4 waves of Add Health (ages 12 to 32)

• Participants in 7th to 12th grade during first wave of study, with follow-up interviews 1 year later, 7 years later, and 13 years later

• Contractual data; N=12,051 with 39,063 total person-records

Data Preparation

Measures

• Outcome: Multiple partners in past year

• Predictor– Past year Heavy Episodic Drinking

(Any/None)

Male95% CI Male

Female95% CI Female

Male95% CI Male

Female95% CI Female

TIME-VARYING PREDICTORS OF RISKY SEX OVER TIME IN A RELATIONSHIP

Example 2

Sample Questions

• How do odds of using a condom change over time from the first to 120th week of a relationship?

• How does the association between contraceptive attitudes and condom use change over time?

Method

• Data from the Relationship Dynamics and Social Life (RDSL) Study

• 1,003 women aged 18-20 (35% African American, Mage=18.7)

• Followed weekly for 2.5 years– Up to 130 occasions per person– Used occasions when in a relationship

between 0 and 130 weeks in duration• 29,823 occasions, 608 individuals

Measures

• Outcome: Weekly condom use

• Predictors– Baseline Contraceptive Attitudes (6-item

scale)

Estimate95% CI

Estimate95% CI

Summary

• Rates and predictors of risky sexual behavior can change over time

• TVEM can help uncover processes unfolding in continuous time

• Prevention programs should target predictors relevant to individuals’ ages and stages of a relationship

Acknowledgments

• Grants 2T32DA 017629 and P50-DA010075-17

• Add Health funded by: P01-HD31921 • RDSL funded by: R01 HD 050329 • Thanks to Nicole Butera, John Dziak,

Yasmin Kusunaki, Michael Yang