Table 3.
Analysis of Survival Curves of Wild-Type and mGsta4-Null Mice
| Wild Type | mGsta4 Null | |
| Gehan–Wilcoxon test for survival curves | ||
| Chi-square | p = .01 | |
| Randomization | p = .018 | |
| Log-rank test for survival curves | ||
| Chi-square | p = .096 | |
| Randomization | p = .102 | |
| Gompertz parameter A (95% confidence interval) | 4.36 × 10−5 (1.47–12.99) × 10−5 | 0.49 × 10−5 (0.10–2.41) × 10−5 |
| Likelihood ratio test for parameter A | p = .020 | |
| Gompertz parameter G (95% confidence interval) | 6.01 × 10−3 (4.72–7.65) × 10−3 | 8.35 × 10−3 (6.64–10.50) × 10−3 |
| Likelihood ratio test for parameter G | p = .047 | |
Notes: Survival curves (n = 50 mice per group; same animals as used for experiment summarized in Table 2) were compared by the Gehan–Wilcoxon and the log-rank tests, as implemented in the NCSS statistical software package. The p values are listed for both the chi-square approximation and the permutation (105 Monte Carlo samples) variants of each test. Maximum likelihood estimates of Gompertz parameters were obtained using the WinModest program (36,37). The values of these parameters for wild-type and mGsta4-null mice were compared by the likelihood ratio test of WinModest. In this test, the log likelihood estimate of the full model is subtracted from that of a “null hypothesis model” in which one of the parameters has been constrained to be identical for the two groups of mice. The resulting difference, multiplied by 2, is distributed as a chi-square random variable with 1 df.