title: Could misreporting of condom use explain the observed association between injectable hormonal contraceptives and HIV acquisition risk?
abstract: OBJECTIVE
  Some observational studies have suggested an association between the use of hormonal contraceptives (HC) and HIV acquisition. One major concern is that differential misreporting of sexual behavior between HC users and nonusers may generate artificially inflated risk estimates.
  
  
  METHODS
  We developed an individual-based model that simulates the South African HIV serodiscordant couples analyzed for HC-HIV risk by Heffron et al. (2012). We varied the pattern of misreporting condom use between HC users and nonusers and reproduced the trial data under the assumption that HC use is not associated with HIV risk. The simulated data were analyzed using Cox proportional hazards models, adjusting for the reported level of condom use.
  
  
  RESULTS
  If HC users overreport condom use more than nonusers, an apparent excess risk could be observed even without any biological effect of HC on HIV acquisition. With 45% overreporting by HC users (i.e., 9 out of every 20 sex acts reported with condoms are actually unprotected) and accurate condom reporting by nonusers, a true null effect can be inflated to give an observed hazard ratio (HR̂) of 2.0. In a different population with lower overall reported condom use, artificially high HR̂s can only be generated if non-HC users underreport condom use.
  
  
  CONCLUSIONS
  Differential condom misreporting can theoretically produce inflated HR̂ values for an association between HC and HIV even without a true association. However, to produce a doubling of HIV risk that is entirely spurious requires substantially different levels of misreporting among HC users and nonusers, which may be unrealistic.
  
  
  CONCLUSIONS
  Considerably differential amounts of condom use misreporting by HC users and nonusers would be needed to produce entirely spurious observed levels of excess HIV acquisition risk among HC users when there is actually no true association.
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, UK.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Smith
authors.affiliation: Department of Global Health, University of Washington, Seattle, USA. Electronic address: rheffron@uw.edu.
authors.forename: Renee
authors.initials: R
authors.lastname: Heffron
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, UK.
authors.forename: Ailsa R
authors.initials: AR
authors.lastname: Butler
authors.affiliation: Department of Global Health, University of Washington, Seattle, USA; Department of Epidemiology, University of Washington, Seattle, USA; Department of Medicine, University of Washington, Seattle, USA.
authors.forename: Connie
authors.initials: C
authors.lastname: Celum
authors.affiliation: Department of Global Health, University of Washington, Seattle, USA; Department of Epidemiology, University of Washington, Seattle, USA; Department of Medicine, University of Washington, Seattle, USA.
authors.forename: Jared M
authors.initials: JM
authors.lastname: Baeten
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, UK.
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Hallett
mesh_terms: D035843:Biomedical Research / Q000379:methods; D003075:Coitus; D017280:Condoms / Q000706:statistics & numerical data*; D003267:Contraception / Q000379:methods*; D003268:Contraception Behavior / Q000706:statistics & numerical data*; D003278:Contraceptives, Oral, Hormonal / Q000008:administration & dosage*; D005260:Female; D015658:HIV Infections / Q000453:epidemiology / Q000635:transmission*; D059147:HIV Serosorting; D006801:Humans; D008297:Male; D064887:Observational Studies as Topic; D016016:Proportional Hazards Models; D018570:Risk Assessment / Q000379:methods
chemical_list: D003278:Contraceptives, Oral, Hormonal
keywords: Condom use; DMPA; HIV; Injectable hormonal contraceptives; Mathematical modelling; Misreporting bias