
ORD PLOTName:
If x and n_{x} denote the class value and the corresponding class frequency, then the Ord plot is a plot of
If this plot is approximately linear, then it can help distinguish between these four distributions based on the following table:
The slope and intercept can be determined by fitting a line to the plotted points. We follow the suggestion of Friendly of using the weights
This compensates for the fact that classes with small frequency have large variance. The primary disadvantage of this plot is that a discrepant frequency affects the points for both x and x+1. For this reason, the Ord plot does not have good resistance properties.
where <y> is a response variable; and where the <SUBSET/EXCEPT/FOR qualification> is optional. This syntax is used for the case where you have raw data. Dataplot will automatically create the frequency table.
where <y> is a variable containing frequencies; <x> is a variable containing the class value; and where the <SUBSET/EXCEPT/FOR qualification> is optional. This syntax is used for the case where your data is already in the form of a frequency table.
ORD PLOT Y X
PPA1  the slope of the fitted line
. Data from p. 47 of Friendly read x y 0 109 1 65 2 22 3 3 4 1 end of data . title case asis title offset 2 label case asis title Ord Plot y1label Frequency Ratio x1label x . tic offset units screen tic offset 3 3 xlimits 1 4 major xtic mark number 4 minor xtic mark number 0 . character x blank line blank dotted . ord plot y x
 
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Date created: 7/25/2007 