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    Outlier Math

    Illustration

    Illustration

    Basic definition

    In statistics, an outlier is a point in a sample that has a substantially different value from the rest.

    Detailed definition

    An outlier is an observation that lies outside the overall pattern of a distribution. 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 an 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. Outliers of this type can be easily identified on a scatter diagram.

    Related terms

    histogram | least squares fitting | scatter diagram

    Educational grade level

    high school level (AP statistics, California grade 4 standard)

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