There are two types of pumps and we want to determine if one is longer lasting then the other. We have been using both types of pumps in the plant for a few years and have complete time to failure data (time from installation to failure). In this simple example all of the pumps from both brands have failed. Brand X (failure time in months) 342 6 2 Brand Y (failure time in months) 4 7 5 10 6 8 Test whether the Brand Y is lasting longer than Brand X using Mann Whitney U test