A Step by Step Guide for SPSS and Exercise Studies

Statistical tests 87
Dialog box 69
Residual plot produces a matrix scatterplot of the observed against the predicted
and standardised residuals. If the homogeneity assumption is satisfied, the plots
should not show any systematic effect, such as a linear relationship between
means and variances, or non-random patterns in the residual plots. In the
Significance level box at the bottom of Dialog box 70 you can decrease the level
of significance used in the post-hoc comparisons to prevent Type I error (see the
relevant discussion in One-way ANOVA of the Analyze menu). Click Continue.
The Save option of Dialog box 69 creates new variables in the data file
(Dialog box 71). Under Predicted Values, you can create a variable showing, for
each case, the Unstandardized predicted value of the dependent variable. You
can also request the Standard error of the Predicted values. The two measures
under Diagnostics (Cook’s distance and Leverage value) show the degree to
which residuals would change if a particular case was deleted. It is wise to delete
cases with large values on any of the Diagnostics measures. Lastly, under
Residuals you can save in the data file the Unstandardized and Standardized
residuals (i.e., differences between the actual values of the dependent variable
and those predicted by the independent variables). You can also save the
Studentized residuals which represent the ratio of Unstandardized residual to an
estimate of the standard deviation of the residual of a particular case. Studentized
residuals have the advantage of taking into account differences in variability
from case to case. Lastly, Deleted residuals represent the Studentized residuals
of a particular case when this case has been excluded from the analysis (Norusis,
1998).