Suppose that we have generated two classification models, M1 and M2, from our data. We have performed 10-fold cross-validation to obtain a mean error rate8 can we determine which model is best? It may seem intuitive to select the model with the lowest error rate; however, the mean error rates are just estimates of error on the true population of future data cases. There can be considerable variance between error rates within any given 10-fold cross-validation experiment. Although the mean error rates obtained for M1 and M2 may appear different, that difference may not be statistically significant. What if any difference between the two may just be attributed to chance? This section addresses these questions.