Friedman Rank Sum Test

The Friedman rank sum test is appropriate for data arising from an unreplicated complete block design, i.e., one in which exactly one observation was collected from each experimental unit, or block, under each treatment. The elements of y are assumed to consist of a groups effect, plus a blocks effect, plus independent and identically distributed residual errors. The interaction between groups and blocks is assumed to be zero.

In the context of a two-way layout with factors groups and blocks, a typical null hypothesis is that the true location parameter for y, net of the blocks effect, is the same in each of the groups. The alternative hypothesis is that it is different in at least one of the groups.

To perform a Friedman rank sum test

Choose Statistics __image\ebd_ebd35.gif Compare Samples __image\ebd_ebd36.gif k Samples __image\ebd_ebd37.gif Friedman rank sum . The dialog shown below appears.

__image\friedman.gif

The Friedman rank sum test has the following options:

Data

Data Set

Select a data set from the dropdown list or type the name of a data set. You can also type into the Data Set edit field any expression that evaluates to a data set.

Variable

Select the columns of the data set to include in the analysis. To include all columns, select ALL. Making no selection has the same effect since ALL is the default value.

Grouping Variable

Specify a grouping variable to use when resampling observations

Blocking Variable

Specify the factor column that indicates block membership for each response value. This must be a factor variable.

Results

Save As

Enter the name for the object in which to save the results of the analysis.

Print Results

Select this to print out the results of the analysis in the designated output window.

Related S-PLUS language functions

friedman.test, print.htest, menuFriedman