Equivalence of two healthcare costing methods: bottom-up and top-down.

This paper compares two quite different approaches to estimating costs: a 'bottom-up' approach, represented by the US Department of Veterans Affairs' (VA) Decision Support System that uses local costs of specific inputs; and a 'top-down' approach, represented by the costing system created by the VA Health Economics Resource Center, which assigns the VA national healthcare budget to specific products using various weighting systems. Total annual costs per patient plus the cost for specific services (e.g. clinic visit, radiograph, laboratory, inpatient admission) were compared using scatterplots, correlations, mean difference, and standard deviation of individual differences. Analysis are based upon 2001 costs for 14 915 patients at 72 facilities. Correlations ranged from 0.24 for the cost of outpatient encounters to 0.77 for the cost of inpatient admissions, and 0.85 for total annual cost. The mean difference between costing methods was $707 ($4168 versus $3461) for total annual cost. The standard deviation of the individual differences was $5934. Overall, the agreement between the two costing systems varied by the specific cost being measured and increased with aggregation. Administrators and researchers conducting cost analyses need to carefully consider the purpose, methods, characteristics, strengths, and weaknesses when selecting a method for assessing cost.