Kaplan-Meier estimates were used to calculate survival curves.
Differences in survival curves were compared using log-rank statistics.
Cox proportional hazard models were also fit to test differences
in survival. Differences in proportions were tested using a chi-square
test (or Fisher’s exact test). P-values less than 0.05 were considered
statistically significant. Analyses were performed using SPSS 8.0
(Statistical Package for Social Sciences software for Windows; SPSS,
Chicago, IL) and Stata (1999 Stata Statistical Software, release 6.0;
Stata Corp., College Station, TX