Publication date: 05/24/2021

Compare Groups: Statistics

The Statistics report for Compare Groups contains the following reports:

Summary

Group Homogeneity Tests

Model Comparisons

Parameter Estimates

Summary

The Summary report contains a row for each group and for the combined data. Each row shows the number of units that failed and the numbers that were left, interval, or right censored. Each row also gives the corresponding mean and standard error. For more information about how the mean and standard error are computed, see Statistical Reports for Survival Analysis.

Group Homogeneity Tests

The Group Homogeneity Tests report contains results of three tests for equality of the hazard functions across groups. The tests differ in how the observations are weighted over time.

Log-Rank

The Log-Rank test uses equal weights for all time points.

Peto-Peto

The Peto-Peto test uses the survival proportion at each time point for weights.

Wilcoxon

The generalized Wilcoxon test uses the number at risk at each time point for weights. This test is referred to as the Gehan test in Klein and Moeschberger (1997).

For each of the above tests, the report includes the chi-square approximation, the associated degrees of freedom, and the p-value for each test. A small p-value suggests that the groups differ. For more information about these tests and comparisons of failure curves, see Klein and Moeschberger (1997, ch. 7).

Parameter Estimates

The Parameter Estimates outline contains reports entitled Parametric Estimate - <Distribution Name> for each distribution that is fit. For each group, the Parametric Estimate - <Distribution Name> report gives the distribution’s parameter estimates and their 95% level confidence intervals. The confidence level for these intervals is determined by the Change Confidence Level option in the Life Distribution - Compare Groups menu.

Individual Group

The tabs within the Individual Group report contain Life Distribution reports for each individual group. For more information about these reports, see Life Distribution Report and Life Distribution Report Options.

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