# A nonparametric test

All Modules When to Use a Nonparametric Test Nonparametric tests are sometimes called distribution-free tests because they are based on fewer assumptions e. Parametric tests involve specific probability distributions e. The cost of fewer assumptions is that nonparametric tests are generally less powerful than their parametric counterparts i. It can sometimes be difficult to assess whether a continuous outcome follows a normal distribution and, thus, whether a parametric or nonparametric test is appropriate. A non parametric test sometimes called a distribution free test does not assume anything about the underlying distribution for example, that the data comes from a normal distribution. It usually means that you know the population data does not have a normal distribution.

If at all A nonparametric test, you should us parametric testsas they tend to be more accurate. Parametric tests have greater statistical powerwhich means they are likely to find a true significant effect. Use nonparametric tests only if you have to i. Nonparametric tests can perform well with non-normal continuous data if you have a sufficiently large sample size generally items in each group.

Therefore the key is to figure out if you have normally distributed data. For example, you could look at the distribution of your data. If your data is approximately normal, then you can use parametric statistical tests.

Check the skewness and Kurtosis of the distribution using software like Excel See: Skewness in Excel and Kurtosis in Excel A normal distribution has no skew.

Kurtosis refers to how much of the data is in the tails and the center. The skewness and kurtosis for a normal distribution is about 1. Negative kurtosis left and positive kurtosis right If your distribution is not normal in other words, the skewness and kurtosis deviate a lot from 1.

Otherwise you run the risk that your results will be meaningless. Data Types Does your data allow for a parametric test, or do you have to use a non parametric test like chi-square? The rule of thumb is: For interval scales or ratio scales use parametric statistics.

A skewed distribution is one reason to run a nonparametric test. Other reasons to run nonparametric tests: One or more assumptions of a parametric test have been violated.

Every parametric test has a nonparametric equivalent. For example, if you have parametric data from two independent groups, you can run a 2 sample t test to compare means. For example, if you have parametric data from two independent groups, you can run a 2 sample t test to compare means. In this situation, parametric and nonparametric test results can give you different results, and they both can be correct! For the two distributions, if you draw a large random sample from each population, the difference between the means is statistically significant. The T-Test in Dissertation & Thesis Research In dissertation or thesis research, there are two types of inferential statistics: parametric and nonparametric tests.

Your sample size is too small to run a parametric test. Your data has outliers that cannot be removed. You want to test for the median rather than the mean you might want to do this if you have a very skewed distribution.

Those tests both assume that the population data has a normal distribution. Non parametric do not assume that the data is normally distributed. The only non parametric test you are likely to come across in elementary stats is the chi-square test.A non parametric test (sometimes called a distribution free test) does not assume anything about the underlying distribution (for example, that the data comes from a normal distribution).

Statistics Definitions > Non Parametric (Distribution Free) Data and Tests. What is a Non Parametric Test? A non parametric test (sometimes called a distribution free test) does not assume anything about the underlying distribution (for example, that the data comes from a normal distribution).That’s compared to parametric test, which makes assumptions about a population’s parameters (for. Read the latest articles of Journal of the Korean Statistical Society at caninariojana.com, Elsevier’s leading platform of peer-reviewed scholarly literature. The nonparametric test is defined as the hypothesis test which is not based on underlying assumptions, i.e.

it does not require population’s distribution to be denoted by specific parameters. The test is mainly based on differences in medians. Gaussian Processes and Kernel Methods Gaussian processes are non-parametric distributions useful for doing Bayesian inference and learning on unknown functions.

They can be used for non-linear regression, time-series modelling, classification, and many other problems. You are here: Home Nonparametric Tests Nonparametric Tests - One Sample Binomial Test – Simple Tutorial The binomial test is the most simple statistical test there is.

Understanding how it works shouldn't be too hard and will help you understand other statistical tests more easily too.

Parametric tests