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Health Services Research & Development

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2011 HSR&D National Meeting Abstract

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2011 National Meeting

3091 — A Comparison of Longitudinal Cost Modeling Techniques

Smith VA (COE - Durham), Maciejewski ML (COE - Durham), Jackson GL (COE - Durham), Edelman DE (COE - Durham), Olsen MK (COE - Durham)

Objectives:
Longitudinal cost analyses are becoming more common in health services research. When the cost variable is semicontinuous (e.g., a high proportion of patients with zero cost), a range of analytic methods exist for modeling these outcomes. In this study (QUERI RRP-09-407), we describe and compare innovative statistical methods for analyzing VA costs from a longitudinal randomized trial of veterans with diabetes and hypertension. We also provide a roadmap for choosing among these analytic methods.

Methods:
The Group Visits randomized trial (HSRD IIR-03-084) examined the effectiveness of group medical clinics on blood glucose and blood pressure in veterans with comorbid diabetes and hypertension. VA specialty care costs of this cohort were estimated in 6-month intervals over 42-months. A comparison was done of predicted specialty care costs estimated from 1) one-part; 2) uncorrelated two-part; and 3) correlated two-part random effects models developed to determine if specialty care costs differed between treatment and control patients one year prior to trial initiation, in the 12-months during the trial, and in the eighteen months after trial completion.

Results:
The VA specialty care costs of 239 veterans over 42-months were drawn from the VA’s DSS National Data Extract. The proportion of veterans with no specialty care costs varied over time from 6% to 19%, which created ambiguity in the appropriate model choice. The statistical significance of the treatment effect varied by modeling strategy.

Implications:
These three approaches for estimating longitudinal costs produced varying results in analyses of longitudinal cost outcomes among veterans participating in a diabetes self-management trial.

Impacts:
Health services research studies often involve analysis of longitudinal cost outcomes. Results can differ between one-part and two-part models, as well as between correlated and uncorrelated models. Thus, analysts should examine a variety of factors to inform their choice among different analytical approaches when estimating longitudinal costs.


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