The numbers 1, 2,…assigned to a set of objects arranged in order according to some criterion such as increasing numerical value. Many non-parametric tests are based on the use of ranks. If two or more observations are indistinguishable according to the chosen criterion then they are said to have tied ranks; they are usually assigned a rank equal to the average of the ranks that would have been assigned in the absence of ties. The following set of twelve values includes two examples of ties: