18. One or more computer-readable storage units having computer-executable instructions, which when executed perform steps, comprising: classifying atomic events into tasks corresponding to user activities associated with a search engine implementation; selecting at least one of a user satisfaction metric or a user engagement metric for assessing a performance of the search engine implementation with respect to the tasks; and differentiating the performance of the search engine implementation from a benchmark associated with standard search engine implementation performance, including applying the at least one of a user satisfaction metric or a user engagement metric to the tasks to produce a task-based statistical distribution, comparing the task-based statistical distribution with the benchmark to compute a test statistic, and based upon the test statistic, determining whether a performance difference between the search engine implementation and the benchmark is statistically significant.
19. The one or more computer-readable storage units of claim 18 having further computer-executable instructions comprising: comparing the test statistic with a significance level to generate a comparison result; and determining whether the task-based statistical distribution is statistically significant departure from the benchmark.