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Dataplot Vol 2 Vol 1

DIFFERENCE OF SKEWNESS

Name:
    DIFFERENCE OF SKEWNESS (LET)
Type:
    Let Subcommand
Purpose:
    Compute the difference between the skewnesss for two response variables.
Description:
    The skewness measures the lack of symmetry in a response variable. The formula is:

      skew = (SUM(Xi-Xmean)**3/(N-1))/s**3

    with s and n denoting the standard deviation and the number of observations, respectively.

    For the differeence of skewnesss, the skewness is computed for each of two samples then their difference is taken.

Syntax:
    LET <par> = DIFFERENCE OF SKEWNESS <y1> <y2>             <SUBSET/EXCEPT/FOR qualification>
    where <y1> is the first response variable;
                <y2> is the first response variable;
                <par> is a parameter where the computed difference of the skewnesss is stored;
    and where the <SUBSET/EXCEPT/FOR qualification> is optional.
Examples:
    LET A = DIFFERENCE OF SKEWNESS Y1 Y2
    LET A = DIFFERENCE OF SKEWNESS Y1 Y2 SUBSET X > 1
Note:
    The difference of skewnesss statistic is also supported for the following commands:

      DIFFERENCE OF SKEWNESS PLOT Y1 Y2 X
      CROSS TABULATE DIFFERENCE OF SKEWNESS PLOT Y1 Y2 X
      BOOTSTRAP DIFFERENCE OF SKEWNESS PLOT Y1 Y2
      TABULATE DIFFERENCE OF SKEWNESS Y1 Y2 X
      CROSS TABULATE DIFFERENCE OF SKEWNESS Y1 Y2 X
      LET Z = CROSS TABULATE DIFFERENCE OF SKEWNESS Y1 Y2 X1 X2

    Enter

    HELP STATISTIC PLOT
    HELP CROSS TABULATE PLOT
    HELP BOOTSTRAP PLOT
    HELP TABULATE
    HELP CROSS TABULATE
    HELP CROSS TABULATE (LET)

for more information on these plots and commands. Default:

    None
Synonyms:
    None
Related Commands:
    SKEWNESS = Compute the skewness.
    MEAN = Compute the mean.
    STANDARD DEVIATION = Compute the standard deviation.
    KURTOSIS = Compute the kurtosis.
    DIFFERENCE OF MEAN = Compute the difference of means.
    DIFFERENCE OF SD = Compute the difference of standard deviations.
    DIFFERENCE OF KURTOSIS = Compute the difference of kurtosis.
    STATISTICS PLOT = Generate a statistic versus subset plot.
    CROSS TABULATE PLOT = Generate a statistic versus two subsets plot.
    BOOTSTRAP PLOT = Generate a bootstrap plot.
    TABULATE = Perform a tabulation for a specified statistic.
    CROSS TABULATE = Perform a cross tabulation for a specified statistic.
Applications:
    Data Analysis
Implementation Date:
    3/2003
Program:
    SKIP 25 
    READ IRIS.DAT Y1 TO Y4 X 
    . 
    LET A = DIFFERENCE OF SKEWNESS Y1 Y2 
    TABULATE DIFFERENCE OF SKEWNESS Y1 Y2 X 
    . 
    XTIC OFFSET 0.2 0.2 
    X1LABEL GROUP ID 
    Y1LABEL DIFFERENCE OF SKEWNESS 
    CHAR X 
    LINE BLANK 
    DIFFERENCE OF SKEWNESS PLOT Y1 Y2 X 
    CHAR X ALL 
    LINE BLANK ALL 
    BOOTSTRAP DIFFERENCE OF SKEWNESS PLOT Y1 Y2 X  
        
    Dataplot generated the following output.
        
    plot generated by sample program

    plot generated by sample program

Date created: 3/27/2003
Last updated: 4/4/2003
Please email comments on this WWW page to alan.heckert@nist.gov.