Centre-specific or average unit costs in multi-centre studies? Some theoryand simulation

Costing issues are increasingly being addressed in multi-centre studies. In this paper, two methods for collecting costing information are compared wi thin a simulated clinical trial setting. One method estimates average treat ment costs by applying unit costs averaged across treatment centres to cent re-specific volumes of resource use. The second uses centre-specific inform ation for both the unit costs and the resource volumes, and then averages a cross centres. Using a pre-specified production relation between the differ ent volumes of resource use, and simulating changes in unit costs, it is sh own that these two methods result in statistically different estimates of a verage treatment costs. This finding holds, regardless of the degree of sub stitutability between the resource volumes, except when considerable uncert ainty surrounds treatment centre responses to relative changes in unit cost s. The findings suggest that a more cautious approach should be adopted in the collection, calculation and interpretation of treatment costs in multi- centre studies. Copyright (C) 2000 John Wiley & Sons, Ltd.