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Matching on provider is risky

Alexander M Walker1

  • 1World Health Information Science Consultants, Riverside Center, Suite 2-400, 275 Grove Street, Newton, MA 02466, USA. Alec.Walker@WHISCON.com

Journal of Clinical Epidemiology
|July 16, 2013
PubMed
Abstract

Insights

Matching on provider in observational studies can worsen bias, not eliminate it. Researchers must carefully consider controls to avoid reducing the effect of important confounders.

Area of Science:

  • Biostatistics
  • Health Services Research
  • Observational Studies

Background:

  • Confounding bias is a critical concern in observational studies.
  • The degree of bias is influenced by the proportion of treatment variation attributable to confounders and instruments.

Purpose of the Study:

  • To demonstrate how matching on provider can exacerbate, rather than remove, bias.
  • To illustrate the impact of matching on provider in a constructed example.

Main Methods:

  • Analysis of confounding bias in observational studies.
  • Illustrative example of bias introduced by matching on provider for coronary artery bypass graft surgery patients.

Main Results:

  • Matching on provider removes a "benign" source of treatment variability.
  • Unmeasured confounders may become the primary determinants of treatment after matching on provider.

Conclusions:

  • Researchers must clearly articulate the sources of pseudorandom variation in observational studies.
  • Care should be taken not to diminish the impact of crucial confounders through excessive control measures.
Keywords:
Amplification biasComparative effectiveness researchInstrumental variablesMatchingPseudorandomizationUnmeasured confoundersZ-bias

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