Box plots illustrating Wald chi-square statistics from 500 bootstrap samples. Testing associations of (A) B7-H3, (B) survivin, (C) Ki-67, (D) CAIX, (E) IMP3, and (F) B7-H1 expression with RCC-specific death using 1 and up to 10 cores. The lower, middle, and upper horizontal lines that comprise the boxes denote the 25th percentile, median, and 75th percentile of the distribution of test statistics from the 500 bootstrap samples. Using a significance level of 0.05, the critical value for a 1 degree-of-freedom chi-square test statistic is approximately 3.8. B7-H1 was modeled as dichotomous (positive versus negative), whereas B7-H3, survivin, Ki-67, CAIX, and IMP3 were modeled as continuous.