Risk-Based Monitoring and Fraud Detection in Clinical Trials Using JMP and SAS

4.4 Multivariate Analyses

4.4.1 Multivariate Inliers and Outliers

In statistics, most of us are familiar with the term “outlier.” Merriam-Webster defines outlier as “a statistical observation that is markedly different in value from the others of the sample.” In a box plot, an outlier may be identified as a point that exceeds 1.5 times the interquartile range (the distance between first and third quartiles) beyond the first or third quartiles. On the other hand, an “inlier” is a value that lies close to the mean. In a univariate setting, a value close to the mean would not raise any eyebrows; in fact, this is entirely expected. However, as Evans points out, it would be unlikely for an observation to lie near the mean for a large number of variables ...