Probability-Probability Plots
Graphical
Analytic Techniques
Ribbon
bar. Select the Graphs tab.
In the More group, click 2D and from the menu, select Probability-Probability Plots to display
the Probability-Probability Plots
Startup Panel.
Classic
menus. On the Graphs - 2D Graphs submenu, select Probability-Probability Plots to display
the Probability-Probability Plots
Startup Panel.
The Probability-Probability (or P-P) plot is
useful for determining how well a specific theoretical distribution fits
the observed data.
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.
The Probability-Probability Plots Startup Panel contains
six tabs: Quick,
Advanced,
Appearance,
Categorized,
Options
1, and Options
2. The following options are available regardless of which tab is
selected.
OK.
Click the OK button
to produce the graph.
Cancel.
Click the Cancel
button to close the Startup Panel without creating a graph.
Options.
See Options
Menu for descriptions of the commands on this menu.
By Group. Click
the By Group button to display
the By
Group specification dialog box.
Sel
Cond. Click the Sel Cond
button to display the Analysis/Graph
Case Selection Conditions dialog box, 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
and syntax
summary.
Case
Weights. Click the
Case Weights button to display
the Analysis/Graph
Case Weights dialog box, 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.
Graphs
Gallery. Click the Graphs
Gallery button to display
the Statistica Graphs
Gallery dialog box, which is used to easily switch among different
types of graphs.
Updating. Click
the Updating button to display
the following menu commands:
Auto. Select Auto
to disconnect the graph from the graph creation dialog box 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 box 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 box 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 box 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 box 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
box.
See also, Conceptual
Overviews - Probability-Probability Plots.