Quantile-quantile plots compare a set of data with the quantiles of a specified cumulative probability distribution function. The default distribution is the normal distribution.
To generate a QQ Math Plot
Choose Graph One Variable
QQ Math Plot. The dialog shown below appears.
Data page
In the QQ Math Plot dialog, the Data page has the following options:
Data
Data Set
Select a data set from the dropdown list or type the name of a data set. You can also type into the Data Set edit field any expression that evaluates to a data set.
Enter an S-PLUS expression that identifies the rows to use in the analysis. To use all the rows in the data set, leave this field blank.
Variables
Value
Specify the column of values to use in the density.
Conditioning
Select the columns specifying conditioning values.
Save Graph Object
Enter the name for the object in which to save the results of the analysis.
Plot page
In the QQ Math Plot dialog, the Plot page has the following options:
Statistic
Distribution
Specify the distribution used to compute the x-axis values.
Reference Line
Include Reference Line
Check this box to include a reference line is in the plots.
Symbol
Symbol Color Choose the color for symbols.
Symbol Style Choose the symbol style to be used for plot symbols.
Symbol Size Choose the size of the symbol to be used for plot symbols.
When a distribution is chosen, fields for those parameters associated with the distribution are enabled.
Titles page
In the QQ Math Plot dialog, the Titles page has the following options:
Titles
Main Title
Specify a main title to add on the top of the page.
Subtitle
Specify a subtitle to add on the bottom of the page.
Labels
X Axis Label
Specify a label for the x-axis.
Y Axis Label
Specify a label for the y-axis.
Axes page
In the QQ Math Plot dialog, the Axes page has the following options:
Aspect Ratio
Aspect Ratio This controls the size of the axis area within the designated plot area. Specify "Fill Plot Area" to fill the page, "Bank to 45 Degrees" to use the 45-degree banking rule in each panel, or "Specified Value" to specify a numeric value.
Ratio Value A numeric value indicating the ratio of height to width.
Scale
X Scale
The scale to use for placing tick marks on the x-axis.
Y Scale
The scale to use for placing tick marks on the y-axis.
Limits
X Limits
The limits for the x-axis. Specify a minimum and a maximum, separated by a comma. For example: "1, 10".
Y Limits
The limits for the y-axis. Specify a minimum and a maximum, separated by a comma. For example: "1, 10".
Relation
X Relation
Controls the relationship between the x-axes in different panels of a conditioned plot. The default value of "Same" ensures that the horizontal or vertical axes on each panel will be identical. "Sliced" gives the same number of data units to corresponding axes on each panel, ensuring that the number of units per cm. is identical. "Free" results in each panel having an axis that accommodates just the data in that panel. For "Sliced" and "Free", axes will be drawn for each panel, using more space on the display.
Y Relation
Controls the relationship between the y-axes in different panels of a conditioned plot.
Alternating
Alternating X Axes
Determines whether x-axes alternate from one side of the group of panels to the other.
Alternating Y Axes
Determines whether y-axes alternate from one side of the group of panels to the other.
Multipanel page
In the QQ Math Plot dialog, the Multipanel page has the following options:
Layout
Number of Columns/Rows/Pages Control the layout of the panels by specifying the number of columns, rows and pages
Panel Order Choose from Graph Order or Table Order. Graph Order begins drawing panels in the bottom left corner of the graph, to the right and up. Table Order begins drawing panels in the upper left corner and continues right.
Include Strip Labels Check this to include strip labels on panels.
Continuous Conditioning
Number of Panels If the data are continuous, the number of panels is determined by the number specified in this field.
Overlap Fraction Create overlapping intervals by specifying the fraction of data points that are shared across two panels.
Interval Type Choose from Equal Counts or Equal Ranges. Equal Counts places an equal number of data points in each plot. Equal Ranges makes the interval widths all equal.