The Confidence Ellipse Options page of the format graph dialog allows you to add and customize these data objects on graphs with the appropriate data structure.

Required data structure

In order to be able to enable confidence ellipses on your graph, a continuous variable must be assigned to both the X (horizontal) and Y (vertical) axes. This data object will not be available if categorical variables are assigned to these axes, or if the “Rows” and “Columns” options have been selected. In these cases, the following message will be displayed in the Format Graph dialog for this data object:

“The Confidence Ellipses data object cannot be added to this graph because it is incompatible with the current axis variable assignments. Switch to the Axis Variables tab of this dialog to update these assignments.”

Format Options

The checkbox at the top of the options page will allow you to toggle on or off confidence ellipses on the graph. On macOS, this is a toggle as opposed to a checkbox.

Once enabled, you will be able to specify how the data should be grouped in order to generate confidence ellipses. The options here are:

•One for all data

•One for each group defined by a categorical grouping variable

Note that the selection that you make will determine the available options for both Fill Color and Border options of the confidence ellipses.

One for all data

This option will consider all of the data on the graph as a single group, and will generate a confidence ellipse using information from all values to calculate the size, shape, and position of the ellipse.

One for each group defined by a categorical variable

This option will require that you select a categorical grouping variable from the input data. The levels of this categorical variable will be used to assign rows of data to different groups, and a separate confidence ellipse will be generated for each group. Only the data assigned to a given group will be used when calculating the size, shape, and position of the confidence ellipse for that group.

Confidence level

This control allows you to choose from a pre-defined set of confidence levels (90%, 95%, or 99%), or to simply enter your own preferred confidence level. The default value is 95%.

Fill Color Options

There are three primary options to choose from when defining the fill color of confidence ellipses on your graphs:

•None (no fill color for any confidence ellipses)

•Single color (for all confidence ellipses)

•Variable (by group)

The first two of these options are rather self explanatory. If you choose “No fill”, then none of the confidence ellipses on your graph will have any fill color applied. If you choose “Single color”, then you will be able to select a fill color and transparency level. These color and transparency settings will be applied to all confidence ellipses on your graph.

If you chose the option “one [confidence ellipse] for all data” when specifying how many confidence ellipses to generate, then these are the only two options that will be available to you. Because there will only be one confidence ellipse, there’s no need to specify multiple different fill colors!

However, multiple confidence ellipses can be generated for a single graph by selecting the option “one for each group defined by:” and specifying a categorical variable to serve as a grouping variable. One confidence ellipse will be generated from the data for each group defined by that grouping variable. If you chose this option, then you will also be able to select the “Variable (by group)” option for the fill color of the resulting confidence ellipses. When using this option, you may choose a color scheme to apply to the confidence ellipse fill colors, or you may choose a specific group to specify its fill color and transparency.

Border Options

There are three primary options to choose from when defining the border options of confidence ellipses on your graphs:

•None (no border for any confidence ellipses)

•Single color (for all confidence ellipses)

•Variable (by group)

The first two of these options are rather self explanatory. If you choose “None”, then none of the confidence ellipses on your graph will have any border displayeed. If you choose “Single color”, then you will be able to select a border color, transparency level, thickness, and line style. These visual settings will be applied to the borders of all confidence ellipses on your graph.

If you chose the option “one [confidence ellipse] for all data” when specifying how many confidence ellipses to generate, then these are the only two options that will be available to you. Because there will only be one confidence ellipse, there’s no need to specify multiple different sets of border options!

However, multiple confidence ellipses can be generated for a single graph by selecting the option “one for each group defined by:” and specifying a categorical variable to serve as a grouping variable. One confidence ellipse will be generated from the data for each group defined by that grouping variable. If you chose this option, then you will also be able to select the “Variable (by group)” option for the border options of the resulting confidence ellipses. When using this option, you may choose a color scheme to apply to the confidence ellipse border colors, or you may choose a specific group to specify its fill color. For each group, you may also specify different options for border transparency, thickness, and line style. Alternatively, you may use the “Global” dropdown to select multiple groups or all groups at once when specifying these formatting options.