GLM Profile Plots

Profile plots (interaction plots) are useful for comparing marginal means in your model. A profile plot is a line plot in which each point indicates the estimated marginal mean of a dependent variable (adjusted for any covariates) at one level of a factor. The levels of a second factor can be used to make separate lines. Each level in a third factor can be used to create a separate plot. All fixed and random factors, if any, are available for plots. For multivariate analyses, profile plots are created for each dependent variable. In a repeated measures analysis, both between-subjects factors and within-subjects factors can be used in profile plots. GLM Multivariate and GLM Repeated Measures are available only if you have the Advanced Statistics option installed.

A profile plot of one factor shows whether the estimated marginal means are increasing or decreasing across levels. For two or more factors, parallel lines indicate that there is no interaction between factors, which means that you can investigate the levels of only one factor. Nonparallel lines indicate an interaction.

After a plot is specified by selecting factors for the horizontal axis and, optionally, factors for separate lines and separate plots, the plot must be added to the Plots list.

Chart Type
The chart can be a line chart or a bar chart
Error Bars
You can include error bars that represent the confidence interval or a number of standard errors. The confidence interval is based on the significance level specified on the Options dialog.
Include reference line for grand mean
Includes a reference line that represents the overall grand mean.
Y axis starts at 0
For line charts with all positive or all negative values, forces the Y axis to start at 0. Bar charts always start (or include) 0.

Obtaining Profile Plots for GLM

  1. From the menus choose:

    Analyze > General Linear Model

  2. Choose Univariate, Multivariate, or Repeated Measures.
  3. In the dialog box, click Plots.
  4. Select a factor for the horizontal axis.

    Optionally, you can: select factors for separate lines and separate plots.

  5. Click Add to list the combination in the Plots list.

GLM Multivariate and GLM Repeated Measures are available only if you have the Advanced Statistics option installed.