2D Categorized Box Plots - Quick Tab

Graphical Analytic Techniques

Select the Quick tab of the 2D Categorized Box Plots Startup Panel to create categorized box plots quickly using mostly default options. For more advanced options, use the Advanced tab.

Graph type. Select the type of box plot to be plotted from the Graph Type list. Click the desired plot link below to obtain a brief description of that type of graph. Additional graph types are available on the Advanced tab.

Layout. Select the type of layout for the graph(s).

Separate. Select this option button to produce a Separate plot layout (where each subset of cases is displayed in a separate graph) for the categorized plots.

Overlaid. Select this option button to produce an Overlaid plot layout (where all subsets are overlaid in one graph and identified by patterns and colors) for the categorized plots.

Variables. Click this button to display a variable selection dialog box, in which you can select the X and (optional) Y grouping variables, the dependent variable(s) to be displayed in the box plots, and the grouping variable that will be used to categorize values of the dependent variable(s) in each small graph. A list of selected variables is displayed below the Variables button.

If more than one dependent variable is selected, a sequence of graphs (one for each dependent variable) will be produced using the same set of grouping variables.

Note that the selected grouping variables do not have to be categorical variables (e.g., contain codes); you can use one of the methods of categorization to categorize continuous variables. The selection of grouping variables is not necessary if the categories are defined via the Multiple subsets method (see the Advanced tab).

Graph Icon. The graph icon in the lower section, left side of the dialog represents the currently selected Graph Type and the selection of values for the Middle Point, Box, and Whiskers. The graph icon previews these three selections. Note that Box and Whiskers options are available only on the Advanced tab.

Middle point. The options in this group box control the type of value and appearance of the middle point.

Value. The middle point can be either the Mean, Median, Mean/Median (uses the Mean as the middle point, plus it has an added marker for the Median), or Median/Mean (uses the Median as the middle point, plus it has an added marker for the Mean) of the selected variable. The options available for the Box and Whiskers on the Advanced tab depend on this selection.

Style. Use the Style box to control how the middle point is represented (by a Line or Point).

Pooled Variance. This check box is available when you select Mean as the middle point Value (see above). The setting of this check box determines how the standard deviations and standard errors (for the means) are computed from grouped data. When the Pooled Variance check box is selected, Statistica computes the pooled within-group (category) variance for all groups (categories), and uses this value as an estimate of s (Sigma) when computing the standard errors for the means (see, for example, Milliken and Johnson, 1984). Specifically, the program computes the pooled within-group (category) variance as:

spooled2 = 1/(n-k) * [s12 *(n1 -1) + ... + sk2 *(nk -1)]

In this equation, k refers to the k groups in the plot, s12, refers to the variance in the i'th category or group, n1 refers to number of valid observations in the i'th category or group, and n is the overall number of valid observations in the plot.

The standard error of the mean for the i'th group is then computed as:

s.e.(mean) = spooled /square root(ni)

Intervals. Use the options in this group box to choose the method of categorization for the box plot (i.e., for the grouping variable that will be used to categorize values of the dependent variable(s) in each small graph). Each of the methods is discussed in method of categorization. Additional methods of categorization are available on the Advanced tab.