Good Research Practices for Comparative Effectiveness Research: Approaches to Mitigate Bias and Confounding in the Design of Nonrandomized Studies of Treatment Effects Using Secondary Data Sources: The International Society for Pharmacoeconomics and Outcomes Research Good Research Practices for Retrospective Database Analysis Task Force Report—Part II
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Abstract
The goal of comparative effectiveness analysis is to examine the relationship between
two variables, treatment, or exposure and effectiveness or outcome. Unlike data obtained
through randomized controlled trials, researchers face greater challenges with causal
inference with observational studies. Recognizing these challenges, a task force was
formed to develop a guidance document on methodological approaches to addresses these
biases.
The task force was commissioned and a Chair was selected by the International Society
for Pharmacoeconomics and Outcomes Research Board of Directors in October 2007. This
report, the second of three reported in this issue of the Journal, discusses the inherent
biases when using secondary data sources for comparative effectiveness analysis and
provides methodological recommendations to help mitigate these biases.
The task force report provides recommendations and tools for researchers to mitigate
threats to validity from bias and confounding in measurement of exposure and outcome.
Recommendations on design of study included: the need for data analysis plan with
causal diagrams; detailed attention to classification bias in definition of exposure
and clinical outcome; careful and appropriate use of restriction; extreme care to
identify and control for confounding factors, including time-dependent confounding.
Design of nonrandomized studies of comparative effectiveness face several daunting
issues, including measurement of exposure and outcome challenged by misclassification
and confounding. Use of causal diagrams and restriction are two techniques that can
improve the theoretical basis for analyzing treatment effects in study populations
of more homogeneity, with reduced loss of generalizability.