Very Low Birth Weight Hospital Volume and Mortality – An Instrumental Variables Approach

George L Wehby; Fred Ullrich; Yang Xie

doi:10.1097/MLR.0b013e31824e32cf

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Very Low Birth Weight Hospital Volume and Mortality – An Instrumental Variables Approach

Journal article

Peer reviewed

Very Low Birth Weight Hospital Volume and Mortality – An Instrumental Variables Approach

George L Wehby, Fred Ullrich and Yang Xie

Medical care, Vol.50(8), pp.714-721

08/2012

DOI: 10.1097/MLR.0b013e31824e32cf

PMCID: PMC3388172

PMID: 22437621

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https://www.ncbi.nlm.nih.gov/pmc/articles/3388172View

Open Access

Abstract

Background: Previous studies of very low birth weight (VLBW) hospital volume effects on in-hospital mortality have used standard risk-adjusted models that only account for observable confounders but not for self-selection bias due to unobservable confounders. Objective: To assess the effects of hospital volume of VLBW infants on in-hospital mortality while explicitly accounting for unobservable confounders and self-selection bias using an instrumental variables (IV) model. Methods: The sample includes 4553 VLBW infants born in 63 hospitals in 2000-2004 in New Jersey. We use IV analysis with the differences between the patient's distances to the nearest low (<50 VLBW infants annually), moderate (51-100 infants annually), and high (>100 VLBW infants annually)-volume hospitals as instruments. We evaluate several volume measures and adjusted for observable infant and hospital characteristics. Results: We find beneficial volume effects on survival that are significantly underestimated in classic risk-adjusted models, under which low and moderate volumes compared with high volumes increase mortality odds by 1.8 and 1.88 times, respectively (risk ratios of 1.4 and 1.5, respectively). However, using the IV approach, we find that low and moderate volumes increase mortality odds by 5.42 and 3.51 times, respectively (risk ratios of 2.76 and 2.21, respectively). These findings suggest unobservable confounders that increase the selection of infants at a greater mortality risk into higher-volume hospitals. Conclusions: Accounting for unobserved self-selection bias reveals large survival benefits from delivering and treating VLBW infants at high-volume hospitals. This supports policies regionalizing the delivery and care for pregnancies at risk for VLBW at high-volume hospitals.

instrumental variables

neonatal intensive care

hospital volume

Very low birth weight

infant mortality

neonatal mortality

Details

Title: Subtitle: Very Low Birth Weight Hospital Volume and Mortality – An Instrumental Variables Approach
Creators: George L Wehby - Dept. of Health Management and Policy, University of Iowa, 105 River Street, N248 CPHB, Iowa City, IA 52242, Phone: 319-384-5133, Fax : 319-384-5125
Fred Ullrich - Dept. of Health Management and Policy, University of Iowa, Iowa City, IA 52242
Yang Xie - Global Outcomes Research, Merck & Co., Inc., One Merck Drive, WS-2E55, Whitehouse Station, NJ 08889, Phone: 908-423-4091, Fax: 908-775-1688
Resource Type: Journal article
Publication Details: Medical care, Vol.50(8), pp.714-721
DOI: 10.1097/MLR.0b013e31824e32cf
PMID: 22437621
PMCID: PMC3388172
NLM abbreviation: Med Care
ISSN: 0025-7079
eISSN: 1537-1948
Grant note: R03 DE018394-02 || DE / National Institute of Dental and Craniofacial Research : NIDCR
Language: English
Date published: 08/2012
Academic Unit: Preventive and Community Dentistry; Health Management and Policy; Economics; Public Policy Center (Archive)
Record Identifier: 9984064196802771

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