Transferability of economic evaluations: approaches and factors to consider when using results from one geographic area for another

BACKGROUND: Geographic transferability of economic evaluation data from one country to another has the potential to make a more efficient use of national and international evaluation resources. However, inappropriate transferability of economic data can provide misleading results and lead to an inefficient use of scarce health care resources. OBJECTIVES: The objective of this study was to review, summarize and categorize the literature on: (i) factors affecting the geographic transferability of economic evaluation data; and (ii) approaches which have either been proposed or used for transferability. METHODS: A systematic literature review on transferability was conducted. Electronic databases, hand searching and bibliographic searching techniques were utilized. Inclusion criteria for the review included conceptual or empirical papers with mention of factors affecting, or approaches for, transferability of economic evaluation data across geographic locations. Exclusion criteria included papers published prior to 1966, non-English language papers, pure science studies and animal studies. Three databases were involved in the primary search: Ovid MEDLINE, EMBASE, and CINAHL. In addition to the primary search, the Heath Economic Evaluation Database (OHE HEED), the NHS EED database and the EconLit databases were searched. Transferability factors were classified into major and minor categories, a classification of alternative transferability approaches was developed, and the number of empirical studies was catalogued according to this classification. RESULTS: There is a substantial amount of literature on factors potentially affecting transferability. Based on these papers we identified 77 factors and subsequently developed a classification system which grouped these factors into five broad categories based on characteristics of the patient, the disease, the provider, the health care system and methodological conventions. Another 40 studies were identified which attempted to transfer economic evaluation data from one country to another and these were classified according to the sources for clinical efficacy, resource utilization and unit cost data. CONCLUSIONS: There is strong evidence indicating that transferability of economic evaluation data is a difficult and complex task. Approaches which have been used for transferability suggest that, at a minimum, there is a need for country-specific substitution of practice pattern data as well as unit cost data. A limitation of this review relates to the lack of empirical studies which prevents stronger conclusions regarding which transferability factors are most important to consider and under which circumstances.