The key difference between parametric and nonparametric test is that the parametric test relies on statistical distributions in data whereas nonparametric do not depend on any distribution. Non-parametric does not make any assumptions and measures the central tendency with the median value. Some examples of non-parametric tests include Mann-Whitney, Kruskal-Wallis, etc.
Parametric is a statistical test which assumes parameters and the distributions about the population are known. It uses a mean value to measure the central tendency. These tests are common, and therefore the process of performing research is simple.
Definition of Parametric and Nonparametric Test
Parametric Test Definition
In Statistics, a parametric test is a kind of hypothesis test which gives generalizations for generating records regarding the mean of the primary/original population. The t-test is carried out based on the students’ t-statistic, which is often used in that value.
The t-statistic test holds on the underlying hypothesis, which includes the normal distribution of a variable. In this case, the mean is known, or it is considered to be known. For finding the sample from the population, population variance is identified. It is hypothesized that the variables of concern in the population are estimated on an interval scale.
Non-Parametric Test Definition
The non-parametric test does not require any population distribution, which is meant by distinct parameters. It is also a kind of hypothesis test, which is not based on the underlying hypothesis. In the case of the non-parametric test, the test is based on the differences in the median. So this kind of test is also called a distribution-free test. The test variables are determined on the nominal or ordinal level. If the independent variables are non-metric, the non-parametric test is usually performed.
What Is the Difference between Parametric and Non-parametric?
The key differences between nonparametric and parametric tests are listed below based on certain parameters or properties.
| Properties | Parametric | Non-parametric |
| Assumptions | Yes | No |
| central tendency Value | Mean value | Median value |
| Correlation | Pearson | Spearman |
| Probabilistic distribution | Normal | Arbitrary |
| Population knowledge | Requires | Does not require |
| Used for | Interval data | Nominal data |
| Applicability | Variables | Attributes & Variables |
| Examples | z-test, t-test, etc. | Kruskal-Wallis, Mann-Whitney |
| Also, read: |
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