A measure that provides a partial ordering of points (observations) in multidimensional space. One such measure is Tukey depth (also called half-space depth). Multidimensional space is divided in two by a hyperplane passing through the point of interest. The hyperplane is rotated, and the Tukey depth is the minimum number of points recorded in a half-space (one half of the multidimensional space that is separated by a hyperplane from the other half). A value for which the Tukey depth is a maximum is the Tukey median.