Direct Medical Costing for Economic Evaluations: Methodologies and Impact on Study Validity
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OO92-8615/2000 Copyright 0 2000 Drug Information Association Inc.
DIRECT MEDICAL COSTING FOR ECONOMIC EVALUATIONS: METHODOLOGIES AND IMPACT ON STUDY VALIDITY CHRISTOPHER EVANS,PHD Project Director
BRUCECRAWFORD, MA Project Director MAP1 Values, Boston, Massachusetts
Costing is central to any pharmacoeconomic evaluation. Recent guidelines on the conduct of pharmacoeconomic studies have outlined aframework for costs that should be included in any economic evaluation. Little research has been done, however; to compare the different methods of data collection used to derive estimates of direct medical costs. This paper addresses the different techniques used to cost medical care resources and the sources of data: direct from case report forms (CRFs), codable CRFs. bill extraction, cost prediction models, databases, and panel data. It offers insight as to the relative merits and drawbacks of the different procedures and offers guidance as to when it is most appropriate to use the different techniques. The paper concludes with a discussion on how the external and internal validity of studies are impacted by the use of the different costing methodologies. Key Words: Direct medical costing; Economic evaluation
INTRODUCTION
analyses of key parameters, the use of quality adjusted life years (QALYs), and a variety AS THE FIELD OF Pharmacoeconomics has of other analyses that should be performed developed and gained wider acceptance, as part of a standard economic evaluation. there has been an increase in interest in estabThese recommendations have tended to focus lishing basic guidelines for the economic on what is to be included or excluded from evaluation of medical technologies (1-6). an economic evaluation, rather than give Typically, these guidelines have promoted guidance as to how best to collect informathe use of the societal perspective for costs, tion that will be used in a pharmacoeconomic discount rates for study results, sensitivity study. Indeed, there has been little attention to the fact that different data sources may yield different results and that diverse data Presented at the DIA Workshop “Economic Assessment Sources have implications on study validity. in Clinical Trials,’’ November 9-10. 1998, New Orpreviously, we have investigated the use leans, Louisiana. and impact that pane’ data and patient Repint address: Christopher Evans, Pm,MAPI reports may have on study findings. In the Values USA, 15 Court Square, Suite 620, Boston, MA 02108. case of patient self reports, we noted that the I73
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main concern was mostly with problems of validity rather than bias (7). Others have investigated the issue of validity and bias. Ellwein and Drummond (8) maintain that bias may occur in economic evaluations when there is intervention-specific dependence between biological and operational variables, and external validity is compromised insofar as study sites do not represent the population
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