Largely ignored: The impact of the threshold value for a QALY on the importance of a transferability factor

Recently, several checklists have been developed which systematically check the transferability of cost-effectiveness (CE) studies between jurisdictions. Some even provide a quantitative score of the degree of transferability. The interpretation of such a score is, however, difficult. In addition, the threshold value for a QALY is a factor that has been given little consideration in these checklists. The importance of a factor as a cause of between-country differences in CE depends on this threshold: factors that explain most of the differences in CE at a low threshold need not be the same factors at a higher threshold. OBJECTIVES: To compare the impact of nine potential causes of variation in CE of smoking cessation support (SCS), at different thresholds for the willingness-to-pay per QALY (WTP). METHODS: A model-based study compared the cost-effectiveness of SCS between six Western-European countries. For several values of WTP, we investigated the impact of between-country differences in nine factors on the incremental net monetary benefit (INMB). The factors were demography, smoking prevalence, mortality, epidemiology and costs of smoking-related diseases, resource use and unit costs of SCS, utility weights and discount rates. RESULTS: Currently, SCS is not reimbursed in The Netherlands, corresponding to a WTP of a 0. With a WTP below a1000, the factors most responsible for between-country differences in INMB are resource use and unit costs of SCS and the costs of smoking-related diseases. Utility values have little impact. At a threshold above a10,000, between-country differences are primarily due to different discount rates, utility weights and epidemiology of smoking-related diseases (incidence and mortality). Costs of smoking-related diseases have little impact above a20,000. At all thresholds, demography has little impact. CONCLUSIONS: When judging the transferability of a CE study to another jurisdiction, we should consider the between-country differences in threshold values per QALY.