Nonparametric Overlay

The Nonparametric Overlay plot in the Fit Life by X platform appears after the scatterplot. Differences among groups can readily be detected by examining this plot. You can choose different scales for viewing these differences. You can change the interval type on a Nonparametric fit probability plot between Simultaneous and Pointwise (results displayed when Show Nonparametric CI is selected). You can also select whether to show parametric or nonparametric confidence intervals.

Pointwise estimates show the pointwise 95% confidence bands on the plot while simultaneous confidence intervals show the simultaneous confidence bands for all groups on the plot. Meeker and Escobar (1998, ch. 3) discuss pointwise and simultaneous confidence intervals and the motivation for simultaneous confidence intervals in a lifetime analysis.

Wilcoxon Group Homogeneity Test

For this example, the Wilcoxon Group Homogeneity Test, shown in Figure 4.7, indicates that there is a difference among groups. The high chi-square value and low p-value are consistent with the differences seen among the Temp groups in the Nonparametric Overlay plot.

Figure 4.7 Nonparametric Overlay Plot and Wilcoxon Test