Tests for Homogeneity

Select menu: Stats | Statistical Tests | Test for Homogeneity

Equality of variances of residuals is an important requirement for the validity of analysis of variance and regression. This dialog allows the homogeneity of variances in different groups to be assessed using Bartlett’s test.

After you have imported your data, from the menu select
Stats | Statistical Tests | Test for Homogeneity.
Fill in the fields as required then click Run.

You can save the results by clicking Store.

This test is rather sensitive to departures from Normality (another requirement for the validity of these analyses) so we recommend that you also examine the residuals. When the test is run it creates tables of variances and replications from which the degrees of freedom are calculated. The test statistic is calculated as M/C, where

M = ∑ ni * log( ∑{ ni * si } / ∑{ ni } ) – ∑{ ni * log( si ) }
C = 1 + ( 1 / ( 3 * (N – 1) ) ) * ( ∑{ 1/ni } – 1 / ( ∑ ni ) )

N = number of groups
ni = degrees of freedom of group i
si = variance of group i

Available data

A list of data structures appropriate to the current input field. The contents will change as you move from one field to the next. Double-click on a name to copy it into the input field, or type the name in directly.

Data

A variate containing the data from which variances are calculated.

Groups

A list of factors defining the groups whose variances are to be compared. The button allows multiple selections to be copied from Available data.

Display

Test	Test statistics.
Variances	Tables of variances and associated degrees of freedom.

Action buttons

Run	Run the analysis.
Cancel	Close the dialog without further changes.
Defaults	Right-click this button to display a shortcut menu that lets you reset the latest user stored defaults or the Genstat default settings.
Store	Opens a dialog where you can store results from the test.

Action Icons

	Pin	Controls whether to keep the dialog open when you click Run. When the pin is down the dialog will remain open, otherwise when the pin is up the dialog will close.
	Restore	Restore names into edit fields and default settings.
	Clear	Clear all fields and list boxes.
	Help	Open the Help topic for this dialog.