What does nonparametric mean?
Nonparametric describes statistical methods, tests, and analyses that do not assume the data follow a particular distribution, such as a normal or Gaussian distribution. Instead of imposing a specified model in advance, these methods often rely on ranks, orderings, or other features of the data that require fewer distributional assumptions. The term is especially useful when sample sizes are small, measurements are heavily skewed, or the distribution of the data is uncertain. In research writing, nonparametric is commonly associated with a test, method, model, or resampling technique. Its advantage is flexibility, although this does not mean that a nonparametric analysis is assumption-free or automatically superior. The contrast is with a parametric approach, which explicitly uses a particular distributional model.
adjectiveDenoting a statistical method, test, or analysis that does not assume the data follow a specified parametric distribution, such as a normal distribution.
- Relating to or involving statistical methods that do not assume a specified form for the underlying probability distribution.
"The researchers used a nonparametric test because the sample size was too small to justify assuming a normal distribution."
"The nonparametric analysis was chosen to avoid making strong distributional assumptions about the data."
"In medical research, a nonparametric test may be preferable when scores are skewed or contain extreme values."
A nonparametric test lets the data speak without requiring them to fit a predetermined statistical curve.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does nonparametric come from?
The word combines the prefix non-, meaning not or without, with parametric, which ultimately derives from parameter. Parameter entered English through Latin from Greek parametron, associated with measuring or setting limits. In statistical terminology, nonparametric developed to describe methods that do not require a specified parametric distribution.
How nonparametric is actually used
Primarily a technical statistical term, usually written as one word; the hyphenated form non-parametric is also encountered. Outside specialist writing, it may need brief explanation.
Easily confused with nonparametric
A parametric analysis assumes that the data follow a specified distribution or model, whereas a nonparametric analysis does not impose that assumption.