Use the Log-Rank and Wilcoxon tests to compare the survival curves of two or more data sets. Each test detects different types of differences between the survival curves; therefore you should use both tests to help determine whether the survival curves are equal.

·    The Log-Rank test compares the actual and expected number of failures between the survival curves at each failure time.

·    The Wilcoxon test is simply a log-rank test weighted by the number of items still surviving at each time point. Therefore, the Wilcoxon test weights early failure times heavier.

For the iron cord data, the test is to determine whether or not the survival curves for the new and old iron cords are the same. Because the p-value for both tests is 0.000 and less than an implied a-value of 0.05, you can conclude that a significant difference exists between the survival curves.