• 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

• 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)

• Parametric Statistical Analysis

1. Gaddis ML et al. Introduction to biostatistics: part 1, basic concepts. Ann Emerg Med 1990;19:86-89.

Editors:

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

Last Reviewed:  July 2015