Analysis of covariance (ANCOVA): Model

The Model dialog provides options for specifying the effects to be analyzed.

Specify model
You can analyze a full factorial model (all main effects for covariates, and all main effects and interactions among factors), a custom model (subset of interactions and main effects), or specify particular terms (for example, for nested designs).
Full factorial
A full factorial model contains all factor main effects, all covariate main effects, and all factor-by-factor interactions. It does not contain covariate interactions. By default, a full factorial model is analyzed (when neither Generate terms nor Write terms are selected).
Generate terms
The model depends on the nature of your data. Clicking Generate terms allows you to select the main effects and interactions that are of interest in your analysis. For more information, see Generate terms and Write terms.
Write terms
Select to include nested terms or when you want to explicitly build any term variable-by-variable. For more information, see Generate terms and Write terms.
Intercept
The intercept is the estimate of the dependent variable when all independent variables are 0. If you can assume that the data pass through the origin, you can exclude the intercept.
Include intercept in model
The intercept is usually included in the model. If you can assume that the data pass through the origin, you can exclude the intercept.
Sum of squares
The method of calculating the sums of squares. For balanced or unbalanced models with no missing cells, the Type III sum-of-squares method is most commonly used. For more information, see Sum of squares.

Specifying models for Analysis of covariance (ANCOVA)

  1. From the menus choose:

    Analyze > Group comparison - parametric > Analysis of covariance (ANCOVA)

  2. In the Analysis of covariance (ANCOVA) dialog, expand the Additional settings menu and click Model.
  3. In the Model dialog, select Generate terms.
  4. In the Generate terms dialog, select a method for building the terms from the Type drop-down menu. For more information, see Generate terms and Write terms.
  5. Select one or more factor or covariate variables or a combination of factor and covariate variables.
  6. Repeat until you have all of the terms that you want in the model. Do not use the same term more than once in the model.
  7. Click OK when finished. You are returned to the Model dialog.
  8. From the Model dialog, select a type of sums of squares and whether or not you want the include the intercept in the model. For more information, see Sum of squares.