Graphs of Input Data - Probability Plot by ...

These Graphs of Input Data plots visualize the normality of the distribution of the currently highlighted variable. The assumption of normality (the data follow a normal distribution) is a very important assumption in statistics (see Elementary Concepts), and normal probability plots are often used to visually verify this assumption.  When you select this option, you can choose from three different types of normal probability plots to examine the normality of values of a variable as categorized by a grouping variable (see also, Categorized Normal Probability Plots).

In some spreadsheets the selection of the grouping variable is predetermined by some global grouping variable (i.e., the grouping variable designated in an analysis dialog). When this is the case, STATISTICA will incorporate the (predetermined) grouping variable name in the appropriate Graphs of Input Data option (e.g., Probability Plot by Gender). In most other cases, STATISTICA will prompt you to select the grouping variable via the Select Variable dialog.

When you are prompted to select a grouping variable that will be used to categorize the values of the currently highlighted variable, the Select Variable dialog will be displayed. Once you have selected the grouping variable from this dialog, another dialog will be displayed (Codes dialog) prompting you to enter the values (codes) for the previously-specified grouping variable (if you leave the list of codes empty, all distinctive values of the grouping variable will automatically be used). After the codes have been entered, a plot displaying separate probability plots for each category of the grouping variable will be produced.

Normal Probability plot. This option produces standard normal probability plots for each category of the currently highlighted variable. For more information on how the standard normal probability plot is constructed, see Normal Probability Plots.  

Half-Normal Probability plot. For more information on how the half-normal probability plot is constructed, see Half-Normal Probability Plots.  

Detrended Normal Probability plot. For more information on how the detrended normal probability plot is constructed, see Detrended Normal Probability Plots.  

Many other types of probability plots are available in STATISTICA's Graphs menu graphs. In order to produce normal probability plots of the values in cases (and not variables), use either the Graphs of Block Data - Custom Graph for Entire Row or Graphs of Block Data - Custom Graph from Block by Row option from the spreadsheet shortcut menu (instead of transposing your data set). Note that if more than one row is highlighted, then a multiple normal probability plot will be produced. For a general overview of the graphics facilities in STATISTICA, see Graphs in STATISTICA.