how to figure an outlier
Usually, the presence of an outlier indicates some sort of problem. This can be a case which does not fit the model under study, or an error in measurement. Outliers are often easy to spot in histograms. For example, the point on the far left in the above figure is an outlier. A convenient definition of a outlier is a point which falls more than 1.5 times the interquartile range above the third quartile or below the first quartile. Outliers can also occur when comparing relationships between two sets of data.
However, this is not definitive and in some cases other definitions will be used. Outliers are basically numbers, in a set of numbers, that don't belong in that set and/or that stand out. For example, in the data set {3, 5, 4, 4, 6, 2, 25, 5, 6, 2} the value of 25 is an outlier. For a set of numerical data (a set of numbers), any value (number) that is markedly smaller or larger than other values is an outlier. This is the qualitative definition.