1. The Effect of a Conditional Cash Transfer for HIV Prevention on Young Women’s Experience of Partner Violence  
Evidence from a randomized experiment in South Africa HPTN 068
K. Kilburn1, A. Pettifor2,3, J. Edwards2, A. Selin2, S. Delong2, R. Twine3, J. Hughes4, J. Wang4, X. Gomez-Olive3, C. MacPhail3,5, K. Kahn3
1University of North Carolina at Chapel Hill, Global Health and Infectious Diseases, Chapel Hill, United States, 2University of North Carolina at Chapel Hill, Epidemiology, Chapel Hill, United States, 3University of the Witwatersrand, MRC/Wits Rural Public Health and Health Transitions Research Unit (Agincourt), Johannesburg, South Africa, 4Statistical Center for HIV/AIDS Research and Prevention (SCHARP), Seattle, United States, 5University of New England, Armindale, Australia
Kelly Kilburn, PhD
Institute for Global Health and Infectious Diseases
University of North Carolina at Chapel Hill
July 25, 2017

2. Conflict of Interest
There are no conflicts of interest to declare.

3. Cultural and social gender norms play a large role
In South Africa, intimate partner violence (IPV) is exceptionally common:
Nationally around 1/3 of women have experienced physical violence by a partner
Cultural and social gender norms play a large role
Prevalence of HIV among young women in our study location:
5.5%: ages 15-19
27%: ages 20-24
References:
Gass JD, Stein DJ, Williams DR, et al. Intimate partner violence, health behaviours, and chronic physical illness among South African women. SAMJ: South African Medical Journal. 2010;100(9):582–585. 
Gómez-Olivé FX, Angotti N, Houle B, Klipstein-Grobusch K, Kabudula C, Menken J, Williams J, Tollman S, Clark SJ. Prevalence of HIV among those 15 and older in rural South Africa. AIDS care Sep 1;25(9):

4. Interconnections between IPV and HIV
Societal norms enabling violence & control of women in relationships
Physical violence in relationships
Forced or coerced sex
HIV transmission
1) Direct (if male partner has HIV)
2) Increased risk of HIV transmission
Inability to negotiate safe sex
Risky sexual behaviors
Figure adapted from: Joyner, K., Rees, k. & Honikman, S Intimate Partner Violence (IPV) in South Africa : how to break the vicious cycle. Policy Brief.

5. HPTN 068 CCT Study Design Eligibility: Young women aged 13-20
Enrolled in high school
N=2,533
Randomization (Phase III, 1:1):
Monthly cash transfers of ~US$10 for girls (parents received ~US$20)
IF they attended at least 80% of school days in the previous month
Data collection:
Participants completed an Audio Computer- Assisted Self-Interview (ACASI) and HIV and HSV-2 each visit including and reassessments annually at 12, 24, and 36 months
IPV outcomes
Any sexual IPV is an indicator for whether a girl reported that she was physically forced to have sex when she did not want to in the last 12 months.
Any physical IPV is an indicator for whether a girl experienced any physical violence by an intimate partner in the last 12 months (WHO scale)

6. CCT and IPV Pettifor et al. (2016) found:
No significant effect of CCT on sexual IPV, HIV, or HSV-2
But did find the CCT led to significant risk reduction for any physical IPV by 34% (RR 0.66)
Source: Pettifor A, MacPhail C, Hughes JP, Selin A, Wang J, Gómez-Olivé FX, et al. The effect of a conditional cash transfer on HIV incidence in young women in rural South Africa (HPTN 068): a phase 3, randomised controlled trial. The Lancet Global Health Dec 31;4(12):e

7. Objective for this study
To understand the pathways through which the CCT affected IPV using mediation analysis.
Mediator (M)
IPV (Y)
CCT (X)

8. Statistical Analysis
Estimated ITT impacts of CCT on hypothesized mediators
Mediators: Sexual partnerships past 12 months (sexual debut, number of partners, any partner), sexual relationship power scale, household economic well-being
Estimated controlled direct effects to analyze the degree to which the CCT works through mediators
Regression Model
Longitudinal Data from 3 follow-up visits during the study-period
Binary outcomes estimated using a GEE log-linear model with robust variance, adjusted for baseline age

9. Impact of CCT on Hypothesized Mediators
RR or coefficient
(95% CI)
Observations (N)
Sexual Debut 1,2
RR 0.82*
( )
3,266 (1,589)
Number of sexual partners in the last 12 months
RR 0.87*
(0.79 – 0.97)
4,869 (2,294)
Any sexual partner in last 12 months
RR 0.91*
( )
Over one sexual partner in last 12 months
RR 0.86
( )
Sexual Relationship Power Scale 3
Coef. 0.06
( )
1,852 (1,195)
High Sexual Power 4
RR 1.12
( )
Log Per Capita Expenditure
Coef. 0.03
( )
4,873 (2,294)
Top quartile Per Capita Expenditure
RR 1.09
( )
Notes: Adjusted for age; 1Among those who had not debuted before baseline 2Per person-visit (cumulative risk) 3SRPS, scores ranges from High SRPS is top tercile (>=34) and compared to low or moderate SRPS score. + pvalue<0.10, *pvalue<0.05, **pvalue<0.01, ***pvalue<0.001

10. CDE(M) = E[Y(1,M)] / E[Y(0,M)]
Mediation Analysis
In our study, controlled direct effects (CDE) represent what the hypothetical effect of the exposure (CCT) on the risk of IPV would be if you could impose a mediator intervention.
CDE(M) = E[Y(1,M)] / E[Y(0,M)]
We set our mediators to a more protective level (i.e., reducing sexual partners) and examined the extent to which this pathway mediates the total CCT effect.
Steps using parametric g-formula for mediation:
Fit models for the effect of CCT on IPV through each mediator
Estimated predicted probabilities under each hypothetical intervention
Estimated standard errors from 5000 bootstrap samples

11. Results
Controlled Direct Effects of mediator interventions on physical IPV
Mediator Intervention
Risk (%)
(T=treatment C=control)
Risk Ratio
(95% CI)
No Mediator Intervention
No sexual debut
T= 14.8
0.57
( )
T=18.5
C=27.8
[RR 0.66]
C= 26.2
No sexual partner (past 12 months)
0.53
( )
C= 27.9
Reduce sexual partners by one (past 12 months)
T= 16.2
0.59
( )
C=27.4
Notes: Adjusted for age, baseline level of mediator, and treatment-mediator interactions. Binary outcomes estimated using a GEE log-linear model and robust variance. Number of sexual partners estimated using a linear regression model with standard errors clustered at the individual level. Effects estimated from Monte Carlo sample (N=5,000) with 95% CIs calculated from standard deviations of point estimates.

12. Conclusions
The protective effect of the CCT on physical IPV is due in part to girls choosing not to engage in sexual partnerships, thereby reducing the opportunity for IPV.
There also remains a direct effect CCT on IPV—Why?
Not attributable to school attendance since girls from both arms attended at high levels
Cash can be empowering for young women in poverty gives them independence and enhances status with peers may reduce their need/desire to engage in exploitative relationships
CCTs can have a supporting role for young women’s health and decision-making including the potential to reduce HIV transmission given the critical intersections with IPV.
Highlights how structural interventions can address interconnections among poverty, sexual health, and female empowerment

13. Acknowledgements
Study Investigators Audrey Pettifor (UNC) Kathleen Kahn (MRC/Wits Agincourt) Catherine MacPhail (WrHI/UOW) Xavier Gomez-Olive (MRC/Wits Agincourt) UNC Amanda Selin Aimee Julien Cheryl Marcus Mary Jane Hill Lisa Albert Suchindran Chirayath Harsha Thirumurthy Sudhanshu Handa Joseph Eron Tamu Daniel
HPTN LOC at FHI360
Phil Andrew
Erica Hamilton
Rhonda White
NIMH
Susannah Allison
Dianne Rausch
NIAID
Sheryl Zwerski
Ellen Townley
Paul Sato
Jenese Tucker
HPTN SDMC
Jim Hughes
Jing Wang
Diana Lynn
Laura McKinstry
Lynda Emel
LSHTM
James Hargreaves
MRC/Wits- Agincourt
Ryan Wagner
Stephen Tollman
Rhian Twine
Wonderful Mabuza
Immitrude Mokoena
Tsundzukani Siwelane
Simon Mjoli
Dumisani Rebombo
Edwin Maroga
Senamile Ndlovu
Audrey Khosa
WrHI
Nomhle Khoza
Sinead Delaney
Helen Rees
HPTN Laboratory Center
Susan Eshleman
Estelle Piwowar-Manning
Oliver Laeyendecker
Yaw Agyei
LeTanya Johnson-Lewis