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PharmacoEconomics

, Volume 29, Issue 2, pp 87–96 | Cite as

Consistently Estimating Absolute Risk Difference when Translating Evidence to Jurisdictions of Interest

  • Simon EckermannEmail author
  • Michael Coory
  • Adrew R. Willan
Leading Article Consistently Estimating Risk Difference

Abstract

Economic analysis and assessment of net clinical benefit often requires estimation of absolute risk difference (ARD) for binary outcomes (e.g. survival, response, disease progression) given baseline epidemiological risk in a jurisdiction of interest and trial evidence of treatment effects. Typically, the assumption is made that relative treatment effects are constant across baseline risk, in which case relative risk (RR) or odds ratios (OR) could be applied to estimate ARD. The objective of this article is to establish whether such use of RR or OR allows consistent estimates of ARD.

ARD is calculated from alternative framing of effects (e.g. mortality vs survival) applying standard methods for translating evidence with RR and OR. For RR, the RR is applied to baseline risk in the jurisdiction to estimate treatment risk; for OR, the baseline risk is converted to odds, the OR applied and the resulting treatment odds converted back to risk.

ARD is shown to be consistently estimated with OR but changes with framing of effects using RR wherever there is a treatment effect and epidemiological risk differs from trial risk. Additionally, in indirect comparisons, ARD is shown to be consistently estimated with OR, while calculation with RR allows inconsistency, with alternative framing of effects in the direction, let alone the extent, of ARD.

OR ensures consistent calculation of ARD in translating evidence from trial settings and across trials in direct and indirect comparisons, avoiding inconsistencies from RR with alternative outcome framing and associated biases. These findings are critical for consistently translating evidence to inform economic analysis and assessment of net clinical benefit, as translation of evidence is proposed precisely where the advantages of OR over RR arise.

Keywords

Relative Risk Natalizumab Consistent Estimation Binary Outcome Baseline Risk 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

The authors thank Lloyd Sansom and the Pharmaceutical Benefits Advisory Committee (PBAC) for encouraging improvements in methods for translating evidence during processes of PBAC guideline revision, evaluation and working committees from 2005 to 2010 and the 2006 PBAC Workshop run by Professors Willan and Eckermann. The authors also thank the European International Society for Pharmacoeconomics and Outcomes Research (ISPOR) for the opportunity to present an early version of the paper in Athens 2008, and participants at the 2008 (Barossa Valley) and 2009 (Oxford) Health Economics from Theory to Practice courses for useful feedback. Finally, the authors acknowledge the constructive comments of anonymous reviewers at PharmacoEconomics in improving the paper. Naturally, any remaining errors or omissions remain the responsibility of the authors.

The data, models and methodology used in this research are not subject to any proprietary interests. A.R. Willan is funded by the Discovery Grant Program of the Natural Sciences and Engineering Research Council of Canada (grant number 44868-08). No sources of funding were used to assist in the preparation of this article. The authors have no conflicts of interest that are directly relevant to the content of this article.

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Copyright information

© Springer International Publishing AG 2011

Authors and Affiliations

  • Simon Eckermann
    • 1
    Email author
  • Michael Coory
    • 2
  • Adrew R. Willan
    • 3
  1. 1.Centre for Health Services DevelopmentUniversity of WollongongWollongongAustralia
  2. 2.Cancer Epidemiology Centre, Cancer CouncilCarltonAustralia
  3. 3.SickKids Research Institute and University of TorontoTorontoCanada

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