You are viewing documentation for the old version 2.30 of Analyse-it. If you are using version 3.00 or later we recommend you go to the Median test.

Median

Median test is a non-parametric test for a difference in central location (median) between two or more independent samples.

The requirements of the test are:

  • Two or more independent samples measured on an ordinal or continuous scale.
  • Samples need not be normal and need not have similar shape distributions.


Arranging the dataset

Data in existing Excel worksheets can be used and should be arranged in a List dataset layout or Table dataset layout. The dataset must contain a continuous scale variable and a nominal/ordinal scale variable containing two or more independent groups.

When entering new data we recommend using New Dataset to create a new 2 variables (1 categorical) dataset ready for data entry.

Using the test

To start the test:

  1. Excel 2007:
    Select any cell in the range containing the dataset to analyse, then click Compare Groups on the Analyse-it tab, then click Median.
  2. Excel 97, 2000, 2002 & 2003:
    Select any cell in the range containing the dataset to analyse, then click Analyse on the Analyse-it toolbar, click Compare Groups then click Median.

  3. If the dataset is arranged using the table layout:
    Tick samples to compare in Variable - Groups.

    If the dataset is arranged using the list layout:
    Click Variable to select the dependent variable and click Factor to select the independent variable containing the groups to compare.

  4. Click OK to run the test.

The report shows the number of observations analysed, and, if applicable, how many missing values were excluded. Since the test classifies the observations relative to the combined median, the combined median and the number of observations above and below are shown.

The hypothesis test is shown. The p-value is the probability of rejecting the null hypothesis, that the samples have the same median, when it is in fact true. A significant p-value implies that at least two samples have different medians.

METHOD The p-value is calculated using the Fisher exact test when there are two samples, otherwise the Chi-square test is used (see [1] or [2]).

Further reading & references

  1. Handbook of Parametric and Nonparametric Statistical Procedures (3rd edition)
    David J. Sheskin, ISBN 1-58488-440-1 2003; 517.
  2. Practical Non-parametric Statistics (3rd edition)
    Conover W.J. ISBN 0-471-16068-7 1999; 218-226.

(click to enlarge)