12. The method of claim 11 further comprising determining whether the performance difference between the first search engine implementation and the second search engine implementation is statistically significant.
11. The method of claim 9 , further comprising comparing a mean difference associated with the first distribution and the second distribution with a standard error of the mean difference to compute a ratio indicating a performance difference, based on at least one of user satisfaction and user engagement, between the first search engine implementation and the second search engine implementation.