Issues in the Reporting and Conduct of Instrumental Variable Studies A Systematic Review

Neil M. Davies*, George Davey Smith, Frank Windmeijer, Richard M. Martin

*Corresponding author for this work

Research output: Contribution to journalReview article (Academic Journal)peer-review

75 Citations (Scopus)

Abstract

Instrumental variables can be used to estimate the causal effects of exposures on outcomes in the presence of residual or uncontrolled confounding. To assess the validity of analyses using instrumental variables, specific information about whether underlying assumptions are met must be presented, in particular to demonstrate that the instrument is associated with the exposure but not with measured confounding factors. We systematically reviewed the epidemiological literature in Embase and Medline for articles containing the term "instrumental variable$" to investigate whether reporting of test statistics in studies using instrumental variables was sufficient to assess the validity of the results. We extracted the information each study reported about their instrumental variables, including specification tests used to check assumptions. The search found 756 studies of which 90 were relevant and were included. Only 25 (28%) studies reported appropriate tests of the strength of the associations between instruments and exposure. Forty-four (49%) studies reported associations between the instrumental variables and observed covariates. Studies using instrumental variables had wide confidence intervals and so effect estimates were imprecise. We propose a checklist of information and specification tests that studies using instrumental variables should report. (Epidemiology 2013;24:363-369)

Original languageEnglish
Pages (from-to)363-369
Number of pages7
JournalEpidemiology
Volume24
Issue number3
DOIs
Publication statusPublished - May 2013

Keywords

  • ACUTE MYOCARDIAL-INFARCTION
  • ANDROGEN-DEPRIVATION-THERAPY
  • TREATMENT-SELECTION BIAS
  • ACUTE ISCHEMIC-STROKE
  • ATYPICAL ANTIPSYCHOTIC MEDICATIONS
  • BREAST-CONSERVING SURGERY
  • DESIGNATED TRAUMA CENTERS
  • ACUTE CORONARY SYNDROMES
  • HIP FRACTURE PATIENTS
  • DRUG-ELUTING STENTS

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