The outlier mean has a reasonable power when the distribution is in a location shift, however, its power is remarkably reduced when he distribution is shifted on only a small fraction of observations, due to large asymptotic variances, while this happen frequently in the cancer study. We consider the study of the nonparametric outlier mean (outlier sum) in two aspects. First, the development of asymptotic distribution for establishing a level test or computing value is established. Second, concept of using outliers for statistical inferences may be treated differently from the classical statistical inferences that construct rules based on good data. We study the relation between powers and asymptotic variances of outliers means aiming at drawing principles for choosing outliers - based inference techniques.