Probability-Probability Plots

Graphical Analytic Techniques

Select Probability-Probability Plots from the Graphs - 2D Graphs submenu to display the Probability-Probability Plots dialog. The Probability-Probability (or P-P) plot is useful for determining how well a specific theoretical distribution fits the observed data. This dialog contains six tabs: Quick, Advanced, Appearance, Categorized, Options 1, and Options 2.

In the P-P plot, the observed cumulative distribution function (the proportion of nonmissing values <= x) is plotted against a theoretical cumulative distribution function in order to assess the fit of the theoretical distribution to the observed data. If all points in this plot fall onto a diagonal line (with intercept 0 and slope 1), then you can conclude that the theoretical cumulative distribution approximates the observed distribution well. If the data points do not all fall on the diagonal line, then you can use this plot to visually assess where the data do and do not follow the distribution (e.g., if the points form an S shape along the diagonal line, then the data may need to be transformed in order to bring them to the desired distribution pattern).

In order to create this plot, the theoretical distribution function must be completely specified. Therefore, the parameters for the distribution must either be defined by the user or computed from the data (see the specified distribution for more information on the respective parameters). Note that you can also use the Quantile-Quantile plot to obtain the parameter estimate(s) (for the best fitting distribution from a family of distributions) to be used here.

Graph Gallery. Click the Graph Gallery button to display the STATISTICA Graphs Gallery dialog. Use the Graphs Gallery to easily switch among different types of graphs.

Select Cases. Click the Select Cases button to display the Analysis/Graph Case Selection Conditions dialog, which is used to create conditions for which cases will be included (or excluded) in the current analysis. More information is available in the case selection conditions overview, syntax summary, and dialog description.

Weight. Click the Weight button to display the Analysis/Graph Case Weights dialog, which is used to adjust the contribution of individual cases to the outcome of the current analysis by "weighting" those cases in proportion to the values of a selected variable.

Options. Click the Options button to display the following drop-down menu items:

Output. Select Output to display the Analysis/Graph Output Manager dialog, which customizes the current graph output management of STATISTICA.

Display. Select Display to display the Analysis/Graph Display Options dialog, which customizes the current graph display of STATISTICA.

Create Macro. Select Create Macro to display the New Macro dialog. When making graphs in STATISTICA, all options and output choices are automatically recorded; when you click Create Macro, the complete recording of all your actions will be translated into a STATISTICA Visual Basic program that can be run to recreate the analysis. See Macro (STATISTICA Visual Basic) Overview for further details.

Close Analysis. Select Close Analysis to close all dialogs associated with the graph. Note that result spreadsheets/graphs will not be closed, only graph dialogs will close.

By Group. Click the By Group button to display the By Group specification dialog.

Updating. Click the Updating button to display the following menu commands:

Auto. Select Auto to disconnect the graph from the graph creation dialog and connect the graph directly to the spreadsheet. Any changes in the spreadsheet data (including selection condition changes) will be immediately reflected in the graph.

Manual. Select Manual to disconnect the graph from the graph creation dialog and connect the graph directly to the spreadsheet. Any changes in the spreadsheet data will be reflected in the graph only after a manual update is initiated.

Locked. Select Locked to disconnect the graph from the graph creation dialog and connect the graph directly to the spreadsheet. The graph is linked to the spreadsheet, but will not be updated when the spreadsheet data changes.

Analysis. Select Analysis to connect the graph to the graph creation dialog and disconnect the graph from the spreadsheet. Changes to analysis options (such as fit type) will be applied to all graphs created by the analysis.

Analysis/Updating. Select Analysis/Updating to connect the graph to the graph creation dialog and disconnect the graph from the spreadsheet. The analysis (while open) will update the graph when the spreadsheet data is changed. Once the analysis is closed, the graph will no longer update when the spreadsheet data is changed.

None. Select None to disconnect the graph from both the spreadsheet and graph creation dialog.

OK. Click the OK button to produce the selected graph.

Cancel. Click the Cancel button to close this dialog without creating a graph.