Parametric and Nonparametric: Demystifying the Terms

center, shape and spread and described how the validity of many statistical procedures relies on an assumption of approximate normality. But what do we do if our data are not normal? In this article, we’ll cover the difference between parametric and nonparametric procedures. Nonparametric procedures are one possible solution to handle non-normal data. Definitions If you’ve ever discussed an analysis plan with a statistician, you’ve probably heard the term “nonparametric ” but may not have understood what it means. Parametric and nonparametric are two broad classifications of statistical procedures. The Handbook of Nonparametric Statistics 1 from 1962 (p. 2) says: “A precise and universally acceptable definition of the term ‘nonparametric ’ is not presently available. The viewpoint adopted in this handbook is that a statistical procedure is of a nonparametric type if it has properties which are satisfied to a reasonable approximation when some assumptions that are at least of a moderately general nature hold.