Transplant Statistics: Annual Report

Technical Notes and Analytic Methods
Median Waiting Time While on the Waiting List

Table 1.6 is similar to Table 1.5 but shows "Waiting Time" rather than "Time to Transplant." The differences are that the "Waiting Time" is censored at any removal from the waiting list other than for cadaveric transplant, and that periods of inactive time on the waiting list are discounted from the calculation. If a person receives a living donor transplant, then the time until the transplant is counted as waiting time, but the living donor transplant is not counted as a transplant.

The median waiting times presented in Table 1.6 are estimates of the length of time on the waiting list by which at least 50% of all patients in the category have received a cadaveric donor transplant while they are on the transplant waiting list. The median waiting times are computed for annual cohorts based on the year of entry onto the waiting list. The value N in each table, for each of the years 1991 through 2000, represents the size of each patient-registration cohort.

Waiting time for each registration is defined as the number of days between the date of entry onto the waiting list and one of the following three possibilities: a) August 1, 2001 (the date on which the analysis was run) for those registrations still waiting on that date; b) the date of removal from the waiting list for cadaveric donor transplant; and c) the date of removal from the waiting list for any other reason, including living donor transplant. Periods of inactive time were also discounted from the calculation.

The median waiting time and confidence limit calculations, performed at the 95% confidence level, were computed using the statistical procedure PHREG in version 8.0 of SAS. Using PHREG, the medians and confidence limits were calculated from time to event curves estimated using the Kaplan-Meier method (Kaplan). In order for inactive time to be excluded from the calculation, discontinuous intervals of risk were implemented (Therneau).