Equality of variances of residuals is an important requirement for the validity of analysis of variance and regression.
This menu allows the homogeneity of variances in different groups to be assessed using Bartlett's test. This test is
rather sensitive to departures from Normality (another requirement for the validity of these analyses);
so it is recommended that the residuals also be examined. When the menu is run tables of variances, and of 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
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.
Available Data
This lists 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 to the
current input field; alternatively, you can type the name directly into the input field.
Display
| Test | Test statistics. |
| Variances | Tables of variances and associated degrees of freedom. |
Action Buttons
| Run | Run the analysis. |
| Cancel | Close the menu without further changes. |
| Defaults | Set the menu settings back to the default settings.
Clicking the right mouse on this button produces a shortcut menu where you can choose to set
the menu using the currently stored defaults or the GenStat default settings. |
| Store | Opens a dialog where you can store results from the test. |
See Also