EBM Consult

Nonparametric Statistical Analysis


    • Refers to the use of statistical tests or methods when the data being studied comes from a sample or population of people that does not follow a normal distributed.
    • Assumes patient population being studied is not normally distributed (i.e., as seen with outliers)
    • Type of data: Nominal or Ordinal. 
      • Nominal:
        • When numbers are assigned to characteristics for the purpose of data classification.  Does not have a sense of order or rank.
      • Ordinal:
        • When numbers are assigned to data that a sense of rank or order, but the magnitude of difference between those numbers is not known.
    • The usual central measure is a median
    Examples of Nonparametic Statistical Tests

    • Mann-Whitney test (assumes 2 independent groups (i.e., not related) being studied)
    • Kruskal-Wallis test (assumes > 2 independent groups being studied/compared)
    • Spearman (correlation test)
    1. Gaddis ML et al. Introduction to biostatistics: part 1, basic concepts. Ann Emerg Med 1990;19:86-89.
    Editors & Reviewers


    • Anthony J. Busti, MD, PharmD, FNLA, FAHA

    Last Reviewed:  July 2015