Computing P-values for a class of permutation tests of equal survival functions

Dallas and Rao (Biometrics 56 (2000) 154) proposed a class of permutation tests for testing the equality of two survival distributions based on randomly right censored survival time data consisting of both paired and unpaired observations. Data sets of this type can occur frequently in medical settings. Two members of this class were advocated for use due to their generally high power for detecting scale and location shifts in the exponential and log-logistic distributions for the survival times, and improved power over paired data test procedures that disregard unpaired observations. Because the computations for the tests become quite laborious as the sample sizes increase, computing routines are required for practical implementation of these tests. This paper provides computing routines to execute the tests.