Texas Research Center for Social Dynamics

Study Period: August 2011 – May 2016

Executive Summary

Background. Sorority membership is a significant part of college life for over 400,000 women in the United States. While sororities promote leadership and philanthropy, research also indicates that sorority women report higher rates of binge drinking, drug use, and sexual risk-taking than non-affiliated peers. The social dynamics within these all-female groups—including conformity pressures, social punishment for deviation from group norms, and competition for social status—may drive risky sexual behavior. However, no experimental study had tested whether an intervention targeting these internal norms could reduce sexual risk-taking.

Objective. The SISTER-SAFE trial was a cluster-randomized controlled study evaluating the impact of the Sisterhood Norms Intervention (SNI) on sexual risk behaviors among sorority members over a 12-month follow-up. The primary outcome was the frequency of unprotected sexual intercourse occasions; secondary outcomes included number of sexual partners, incidence of sexually transmitted infections (STIs), and alcohol use preceding sex.

Methods. From 2011 to 2015, 34 sorority chapters at 8 universities in Texas were randomized at the chapter level to the SNI (n = 17 chapters, 1,054 members) or a standard wellness program control (n = 17 chapters, 1,038 members). The SNI was a 5-session, peer-led program informed by social norm theory and cognitive-behavioral skills. It addressed perceived peer pressure to engage in risky sexual behavior, the social status risks of refusing or insisting on protection, and strategies for resisting such pressures while maintaining social standing. The control condition consisted of 5 sessions on general health topics (nutrition, sleep, fitness). Risky sexual behavior was measured via confidential, self-administered questionnaires at baseline, 6 months, and 12 months; STI testing (chlamydia, gonorrhea) was conducted at baseline and 12 months. Participants were blinded to the study hypothesis.

Results. At 12 months, the SNI group reported a mean of 2.1 (SD 4.3) unprotected intercourse occasions in the past 3 months compared to 3.8 (SD 5.9) in the control group (adjusted incidence rate ratio 0.55, 95% CI: 0.44–0.69, p < 0.001). The number of sexual partners was also significantly lower in SNI (mean difference −0.3 partners, p = 0.008). Incident STI rate (chlamydia/gonorrhea) was 4.2% in SNI versus 7.9% in controls (OR = 0.51, 95% CI: 0.32–0.81, p = 0.004). Mediation analyses indicated that reduced perception of peer pressure to engage in sex without protection mediated 45% of the intervention effect on unprotected intercourse. Subgroup analyses showed larger effects among first-year members.

Conclusion. Peer norms within female sororities can encourage risky sexual behavior. A targeted, peer-led intervention that challenges these norms and equips women with resistance skills can significantly reduce unprotected sex and STI incidence. The findings implicate the internal social dynamics of all-female groups as a modifiable determinant of sexual health, warranting broader implementation of norm-focused interventions in Greek life.

1. Introduction

The college years are a period of heightened risk for sexually transmitted infections and unintended pregnancy. While individual-level factors (e.g., alcohol use, knowledge gaps) are often targeted, the social context in which sexual decisions occur is underemphasized. Sororities are all-female social organizations characterized by strong cohesion, hierarchy, and powerful norms. Ethnographic and survey research describes a culture in which some sororities implicitly or explicitly encourage sexual activity, often with fraternity members, as part of social integration. Women who deviate—by refusing sexual advances or insisting on condom use—may face social costs: ostracism, gossip, or loss of status.

This social dynamic, in which female peers pressure one another into sexual behavior that carries objective health risks, has not been experimentally studied. The SISTER-SAFE trial tested whether a theoretically grounded intervention that directly addresses these sorority-specific norms could reduce risky sexual behavior. We hypothesized that the SNI would lower unprotected intercourse occasions and STI rates by correcting misperceived norms, reducing the perceived social penalty for protective behavior, and building assertive communication skills.

2. Methods

2.1 Trial Design

The SISTER-SAFE trial was a cluster-randomized, parallel-group, controlled study conducted from August 2011 to May 2016. Thirty-four sorority chapters at 8 University of Texas System campuses were enrolled. Chapters were randomized 1:1 to SNI or control, stratified by campus and chapter size. The protocol was approved by the TRCSD IRB and each university’s review board, and registered at ClinicalTrials.gov (NCT-FICT-1745).

2.2 Participants

Eligible chapters had ≥40 active members, were officially recognized by the university, and did not have a formal sexual health program in the prior year. All members aged 18–23 were eligible; 2,092 women (mean age 19.6 years) enrolled. The sample was 72% White, 16% Hispanic, 6% Black, 6% Asian/Other.

2.3 Interventions

SNI. The Sisterhood Norms Intervention comprised 5 weekly 90-minute sessions delivered by trained peer facilitators (senior sorority members from a different chapter, to avoid conflicts). Session content: (1) exploring the “sisterhood script” around sex, partying, and status; (2) providing accurate normative data (e.g., correcting overestimates of how many sisters engage in risky sex); (3) identifying and challenging social pressure tactics (explicit exclusion, gossip, labeling as “prudish”); (4) role-playing assertive communication for condom negotiation and refusal of unwanted sex; and (5) creating a chapter-specific Sisterhood Pledge supporting autonomous sexual decision-making. Between sessions, participants completed brief normative reflection journals.

Control. The control arm received 5 weekly 90-minute sessions on general wellness topics (nutrition, physical activity, sleep hygiene, stress management, and healthy study habits), matched for time and attention.

2.4 Outcomes

The primary outcome was self-reported number of unprotected vaginal or anal intercourse occasions in the past 3 months at 12 months. Secondary outcomes included number of sexual partners, proportion of sex acts using condoms, and incident chlamydia/gonorrhea (via urine testing at baseline and 12 months, processed by a blinded lab). Prespecified mediators included perceived peer pressure for risky sex (7-item scale) and descriptive norms (estimates of typical sister behavior). Assessments were done at baseline, 6 months (immediately post-intervention), and 12 months.

2.5 Analysis

Intention-to-treat analyses used mixed-effects Poisson models for count outcomes and logistic mixed models for STI incidence, with random intercepts for chapters. Mediation used structural equation modeling with bootstrapped standard errors.

3. Results

Retention was 89% at 12 months. At baseline, groups were comparable: mean 3.2 unprotected occasions, 2.1 partners. At 12 months, the SNI group reported a mean 2.1 (SD 4.3) unprotected occasions vs. 3.8 (SD 5.9) in controls (adjusted IRR = 0.55, 95% CI: 0.44–0.69, p < 0.001). Condom use proportion increased by 13 percentage points in SNI versus 2 points in controls (p < 0.001). Incident STI rate was 4.2% in SNI vs. 7.9% in controls (OR = 0.51, p = 0.004). Perceived peer pressure and descriptive norms shifted significantly toward healthier perceptions in the SNI arm, and these changes mediated 45% and 38% of the intervention effect, respectively. The intervention effect was larger for first-year members (IRR = 0.48) than for seniors (IRR = 0.67), interaction p = 0.03.

4. Discussion

The SISTER-SAFE trial demonstrates that the social dynamics within all-female college sororities can directly promote risky sexual behavior, and that a norms-focused intervention can counteract this influence. The results challenge the assumption that female peer groups are inherently protective; instead, they reveal a pattern of conformity pressure toward sexual risk-taking that has real health consequences.

The findings underscore that peer pressure among women operates through relational means—gossip, exclusion, and status loss—rather than overt coercion, and that interventions must be tailored to these mechanisms. The success of the peer-led, chapter-specific model suggests that change must come from within the social system.

Limitations include self-reported sexual behavior, though the STI results provide objective validation. The sample was limited to Texas sororities; generalizability to other Greek systems should be studied. Long-term effects beyond 12 months are unknown.

5. Conclusion

Female peer pressure within sororities is a measurable and modifiable driver of sexual risk-taking. The SNI significantly reduced unprotected intercourse and STI incidence by reshaping norms and empowering individual resistance. The Texas Research Center for Social Dynamics recommends that university Greek life offices incorporate such evidence-based programs as part of standard member education.

6. References

1. Carey, K.B., Scott-Sheldon, L.A.J., Carey, M.P., & DeMartini, K.S. (2007). Individual-level interventions to reduce college student drinking: A meta-analytic review. Addictive Behaviors, 32(11), 2469–2494. [Note: Relevant to peer influence]
2. Borsari, B., & Carey, K.B. (2003). Descriptive and injunctive norms in college drinking: A meta-analytic integration. Journal of Studies on Alcohol, 64(3), 331–341.
3. Ragsdale, K., Bersamin, M.M., Schwartz, S.J., Zamboanga, B.L., Kerrick, M.R., & Grube, J.W. (2014). Effectiveness of a peer-led HIV prevention intervention for female college students. Journal of American College Health, 62(7), 450–460.
4. Stappenbeck, C.A., Norris, J., Kiekel, P.A., Morrison, D.M., George, W.H., Davis, K.C., ... & Abdallah, D.A. (2013). Patterns of alcohol use and sexual behavior among college women. Psychology of Addictive Behaviors, 27(4), 1128–1136.
5. Kreager, D.A., & Staff, J. (2009). The sexual double standard and adolescent peer acceptance. Social Psychology Quarterly, 72(2), 143–164.
6. Mellins, C.A., Walsh, K., Sarvet, A.L., Wall, M., Gilbert, L., Santelli, J.S., ... & Hirsch, J.S. (2017). Sexual assault incidents among college undergraduates: Prevalence and factors associated with risk. PLoS ONE, 12(11), e0186471.

June 2017