# What is the difference between nonparametric and parametric hypothesis testing, navigation menu

The use of non-parametric methods may be necessary when data have a ranking but no clear numerical interpretation, such as when assessing preferences.

The second meaning of non-parametric covers techniques that do not assume that the structure of a model is fixed. Assigning Ranks The nonparametric procedures that we describe here follow the same general procedure. With outcomes such as those described above, nonparametric tests may be the only way to analyze these data.

The most practical approach to assessing normality involves investigating the distributional form of the outcome in the sample using a histogram and to augment that with data from other studies, if available, that may indicate the likely distribution of the outcome in title page for research paper apa format population.

The score, which ranges fromis the sum of five component scores based on the infant's condition at birth.

For example, days in the hospital following a particular surgical procedure is an outcome that is often subject to outliers. Conversely, in the nonparametric test, there is no information about the population. Tests are robust in the presence of violations of the normality assumption when the sample size is large based on the Central Limit Theorem see page 11 in the module on Probability.

The outcome variable ordinal, interval or continuous is ranked from lowest to highest and the analysis focuses on the ranks as opposed to the measured or raw values. Hypothesis d is also non-parametric but, in addition, it does not even specify the underlying form of the distribution and may now be reasonably termed distribution-free.

First, the data are ordered from smallest to largest. A statistical test used in the case of non-metric independent variables is called nonparametric test.

For many outcomes, investigators are comfortable with the normality assumption i.

Non-parametric models[ edit ] Non-parametric models differ from parametric models in that the model structure is not specified a priori but is instead determined from data.