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Methodological Challenges in Biomedical HIV Prevention Trials (2008) / Chapter Skim
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Appendix D: Methods for Analyzing Adherence
Pages 245-249

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From page 245...
... Comparing Adherence Patterns between Study Arms In this example, assume first that study staff record a summary adherence measure Y for each individual at every clinic visit, and that visits are scheduled at regular intervals, such as monthly. Let the value of Y for individual i at visit t be denoted Yit.
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From page 246...
... Similarly, pregnancy is an indicator of unprotected sex, which will also have an impact on "compliance," because subjects found to be pregnant are commonly taken off product. Whether compliance analyses censor pregnant women at this time, or rather insert zero measures or carry the last observation forward, the resulting patterns should remain similar between study arms under the strong null hypothesis.
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From page 247...
... Thus a comparison between arms of times to HIV infection, adjusted for a subject-specific adherence level, would yield an unbiased measure of the effectiveness of the intervention. Investigators can stratify the analysis on the summary adherence measure, or use it as a baseline covariate in a Cox regression analysis, to obtain adherenceadjusted hazard ratios.
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From page 248...
... In the intervention arm, investigators transform the observed time to HIV infection T via observed adherence A to the latent interventionfree time T0 using a postulated parameter value β. The estimated value of β is found when the back-transformed times in the treatment arm coincide in distribution with the observed times T0 in the control arm.
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From page 249...
... 2005. Structural accelerated failure time models for the effects of observed exposures on repeated events in a clinical trial.
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Key Terms

  • study arms
  • intervention arm
  • adherence measure
  • causal effect
  • control arm

  • adherence level
  • adherence levels
  • summary measures
  • clinical trials
  • randomized intervention

  • adherence patterns
  • comparing adherence
  • adherence measures
  • null hypothesis
  • past week

  • treatment arm
  • observed times
  • average adherence
  • strong null
  • observed time

  • controlled clinical
  • compare daily
  • failure times
  • analyses censor
  • unbiased evaluation

  • randomized interventions
  • handle adherence
  • event times
  • regression analysis
  • actual start


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