vaccines, this interval was assumed to be 2 years. The appropriate interval was incorporated into the discounting calculations.
To estimate the cost of health care associated with each condition, the committee developed a set of “clinical scenarios” that specified the health services required, including hospitalizations, procedures, medications, office visits, rehabilitation services, and long-term institutional care. An appropriate unit of service (e.g., hospital days, doses of medication) was specified, and the amount of care received was defined in terms of those units. Costs, represented by charges for specific services, also were specified in terms of units of service.
For inpatient hospitalizations, hospital costs were estimated by using diagnosis-related group average national payments by the Health Care Financing Administration (HCFA) (St. Anthony’s Publishing, Inc., 1995). Outpatient costs and inpatient physician visits were estimated from HCFA data as well (HCFA, 1995). For these costs, the committee estimated general categories of costs (outpatient physician visit with and without tests, etc.) and applied these to the morbidity scenarios. See Table 5–2 for examples of unit costs.
In addition, for each form of care, the committee specified the proportion of patients within the scenario that received that form of care. It was assumed that all costs of care associated with the condition under study would be averted with vaccine use.
The total cost of each form of care was calculated as
cc=(uc • nc) • pc • ps • N, (12)
where cc is the total cost of type of care c for health state i, uc is the unit cost of this form of care, nc is the number of units of care received, pc is the percentage of patients within the scenario that received this form of care, ps is the percentage of all patients that experience this scenario, and N is the total number of patients with the condition under study.
The cost cc was then discounted to adjust for To, the time from average age at vaccination to average age at onset of the condition, plus tm, the duration of intervening health states that persist for at least 1 year. For continuing care required for a specified multiyear period rather than a period of days or weeks, it was necessary to allow for discounting of the stream of future costs. As in the QALY calculations, these costs were discounted to the beginning of the health state by using the Excel present-value function. For some health states, care continues for the remaining lifetime. The length of the remaining lifetime was estimated from the unadjusted 1993 life table life expectancy value (NCHS, 1993) at the average age at onset of the health state.