Color Map on Correlations

The Color Map on Correlations shows the absolute value of the correlation between any two effects that appear in either the Model or the Alias Terms outline. The cells of the color map are identified above the map. There is a cell for each effect in the Model outline and a cell for each effect in the Alias Terms outline. Smaller values are desired as the values reflect potential bias on the estimate of each model effect (row) from each alias term (column).

By default, the absolute magnitudes of the correlations are represented by a blue to gray to red intensity color theme. In general terms, the color map for a good design shows a lot of blue off the diagonal, indicating orthogonality or small correlations between distinct terms. Large absolute correlations among effects inflate the standard errors of estimates.

To see the absolute value of the correlation between two effects, hover your cursor over the corresponding cell. To change the color theme for the entire plot, right click in the plot and select Color Theme. To save a table of the correlations, right click to the right of the plot below the legend and select Table of Correlations.

Color Map Example

Figure 15.24 shows the Color Map on Correlations for the Bounce Data.jmp sample data table, found in the Design Experiment folder. The deep red coloring indicates absolute correlations of one. Note that there are red cells on the diagonal, showing correlations of model terms with themselves.

All other cells are either deep blue or light blue. The light blue squares correspond to correlations between quadratic terms. To see this, hover your cursor over each of the light blue squares. The absolute correlations of quadratic terms with each other are small, 0.0714.

From the perspective of correlation, this is a good design. When effects are highly correlated, it is more difficult to determine which is responsible for an effect on the response.

Figure 15.24 Color Map on Correlations

Tip: To save a table of the correlations, right click to the right of the plot below the legend and select Table of Correlations.