Comparison of instrumental variable analysis using a new instrument with risk adjustment methods to reduce confounding by indication

Gang Fang; John M Brooks; Elizabeth A Chrischilles

doi:10.1093/aje/kwr448

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Comparison of instrumental variable analysis using a new instrument with risk adjustment methods to reduce confounding by indication

Journal article

Open access

Peer reviewed

Comparison of instrumental variable analysis using a new instrument with risk adjustment methods to reduce confounding by indication

Gang Fang, John M Brooks and Elizabeth A Chrischilles

American journal of epidemiology, Vol.175(11), pp.1142-1151

06/01/2012

DOI: 10.1093/aje/kwr448

PMID: 22510277

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Abstract

Confounding by indication is a vexing problem, especially in evaluating treatment effects using observational data, since treatment decisions are often related to disease severity, prognosis, and frailty. To compare the ability of the instrumental variable (IV) approach with a new instrument based on the local-area practice style and risk adjustment methods, including conventional multivariate regression and propensity score adjustment, to reduce confounding by indication, the authors investigated the effects of long-term control (LTC) therapy on the occurrence of acute asthma exacerbation events among children and young adults with incident and uncontrolled persistent asthma, using Iowa Medicaid claims files from 1997-1999. Established evidence from clinical trials has demonstrated the protective benefits of LTC therapy for persistent asthma. Among patients identified (n = 4,275), those with higher asthma severity at baseline were more likely to receive LTC therapy. The multivariate regression and propensity score adjustment methods suggested that LTC therapy had no effect on the occurrence of acute exacerbation events. Estimates from the new IV approach showed that LTC therapy significantly decreased the occurrence of acute exacerbation events, which is consistent with established clinical evidence. The authors discuss how to interpret estimates from the risk adjustment and IV methods when the treatment effect is heterogeneous.

Multivariate Analysis

Comparative Effectiveness Research - methods

Anti-Asthmatic Agents - therapeutic use

United States

Bias

Humans

Child, Preschool

Male

Long-Term Care

Risk Adjustment - methods

Young Adult

Comparative Effectiveness Research - statistics & numerical data

Adult

Female

Medicaid

Child

Severity of Illness Index

Data Interpretation, Statistical

Treatment Outcome

Asthma - drug therapy

Propensity Score

Regression Analysis

Iowa

Confounding Factors (Epidemiology)

Adolescent

Details

Title: Subtitle: Comparison of instrumental variable analysis using a new instrument with risk adjustment methods to reduce confounding by indication
Creators: Gang Fang - Division of Pharmaceutical Outcomes and Policy, Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, 27599-7573, USA. gang_fang@unc.edu
John M Brooks
Elizabeth A Chrischilles
Resource Type: Journal article
Publication Details: American journal of epidemiology, Vol.175(11), pp.1142-1151
DOI: 10.1093/aje/kwr448
PMID: 22510277
NLM abbreviation: Am J Epidemiol
ISSN: 0002-9262
eISSN: 1476-6256
Publisher: United States
Grant note: U18 HSO16094 / PHS HHS
Language: English
Date published: 06/01/2012
Academic Unit: Pharmacy; Epidemiology
Record Identifier: 9983995117202771

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