Small sample survdiff using permutation reference distributions.
permlogrank(formula, data, subset, na.action, rho=0, nperm=5000)number of permutations for the reference distribution
see survdiff for details
permlogrank is the permutation version of k-sample survdiff. see survdiff in survival package for details.
Heller G, Venkatraman ES. (1996). Resampling procedures to compare two survival distributions in the presence of right censored data. Biometrics 52:1204-1213.