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Potential bias of instrumental variable analyses for observational comparative effectiveness research
Annals of Internal Medicine
|July 16, 2014
Summary
Instrumental variable analysis in comparative effectiveness research (CER) may yield biased results. Unadjusted "instrument-outcome confounders" were found in all reviewed CER studies, questioning their reliability.
Area of Science:
- Health Services Research
- Biostatistics
- Epidemiology
Background:
- Instrumental variable analysis is a common method in comparative effectiveness research (CER).
- It aims to control for unobserved and observed patient characteristics affecting outcomes.
- However, potential bias can arise from unadjusted instrument-outcome confounders.
Purpose of the Study:
- To evaluate the prevalence of potential instrument-outcome confounders in published CER studies using instrumental variable analysis.
- To assess the extent to which these studies adjust for identified confounders.
Main Methods:
- Systematic review of published CER studies employing instrumental variable analysis.
- Literature search for common instrument-outcome pairs and their potential confounders.
- Analysis of identified studies for adjustment of these confounders.
Main Results:
- 187 CER studies using instrumental variable analysis were identified.
- 114 studies used common instrument categories (distance, regional, facility, physician variation).
- Potential unadjusted instrument-outcome confounders were present in all reviewed studies; only 6% adjusted for external confounders.
Conclusions:
- Failure to adjust for instrument-outcome confounders may bias effect estimates in instrumental variable CER studies.
- Overreliance on instrumental variable studies for CER is cautioned due to potential biases.
- Further research is needed to address instrument-outcome confounding in CER.
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