outlier

thumb|Figure 1. Box plot of data from the [[Michelson–Morley experiment displaying four outliers in the middle column, as well as one outlier in the first column.]]

In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to a variability in the measurement, an indication of novel data, or it may be the result of experimental error; the latter are sometimes excluded from the data set. An outlier can be an indication of exciting possibility, but can also cause serious problems in statistical analyses.