In statistics, we consider a random variable in terms of a reliable estimate of its *central value* (center) and *spread* from the center. The center is measured by the mean, and the spread by the standard deviation from the mean. In practice, data samples (such as the usual *judgement* selection of comparables in transfer pricing practice) contain outliers that distort the estimates of mean and standard deviation. As a result, statistical (confidence or tolerance) intervals based on the mean and standard deviation may not be reliable. See Gerald Hahn & William Meeker, *Statistical Intervals* (John Wiley, 1991) for a detailed coverage of tolerance and confidence intervals.