Hello, Some statistical SW packages offer the ability to compare two or more sets of reliability or life data in order to determine which of the data sets has a more favorable life distribution. The data sets could be from two alternate designs, manufacturers, lots, assembly lines, etc. The data sets may contain censored data. In general, the problem boils down to that of being able to determine any statistically significant difference between the two (or more) samples of potentially censored data from two possibly different populations. These tools comes to mind: (a) Contour Plots: To determine whether two data sets are significantly different and at what confidence level, one can utilize the contour plots. By overlaying two contour plots from two different data sets at the same confidence level, one can visually assess whether the data sets are significantly different at that confidence level if there is no overlap on the contours (were the same distribution must be fitted to both data sets). for eample see: http://reliawiki.org/index.php/Comparing_Life_Data_Sets#Contour_Plots (b) Life Comparison Tool: suggested by Gerald G. Brown and Herbert C. Rutemiller, to estimate the probability of whether the times-to-failure of one population are better or worse than the times-to-failure of the second (could be from differnt distributions). The same tool could be used to perform Stress-Strength analysis. For example of life comparion tool see: http://reliawiki.org/index.php/Comparing_Life_Data_Sets#Life_Comparison_Tool For example of Stress-Strength analysis see: http://reliawiki.org/index.php/Stress-Strength_Analysis