DIFFERENCE OF VARIANCE

DIFFERENCE OF VARIANCE (LET)

Let Subcommand

Compute the difference between the variances for two response variables.

The variance is a common measure of the spread of a distribution or variable. The formula is:
\( s = \frac{\sum_{i=1}^{n}{(x - \bar{x})^2}}{n-1} \)

with \( \bar{x} \) denoting the mean.

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

LET <par> = DIFFERENCE OF VARIANCE <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 variances is stored;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.

LET A = DIFFERENCE OF VARIANCE Y1 Y2
LET A = DIFFERENCE OF VARIANCE Y1 Y2 SUBSET X > 1

Dataplot statistics can be used in a number of commands. For details, enter
HELP STATISTICS

None

None

VARIANCE	= Compute the variance.
STANDARD DEVIATION	= Compute the standard deviaition.
MEAN	= Compute the mean.
DIFFERENCE OF MEAN	= Compute the difference of the means.
DIFFERENCE OF SD	= Compute the difference of the standard deviation.
DIFFERENCE OF MAD	= Compute the difference of the median absolute deviation.
DIFFERENCE OF AAD	= Compute the difference of the average absolute deviation.
DIFFERENCE OF IQ RANGE	= Compute the difference of the interquartile range.
STATISTICS PLOT	= Generate a statistic versus subset plot.
BOOTSTRAP PLOT	= Generate a bootstrap plot.
TABULATE	= Perform a tabulation for a specified statistic.

Data Analysis

2003/03

SKIP 25 
READ IRIS.DAT Y1 TO Y4 X 
. 
LET A = DIFFERENCE OF VARIANCE Y1 Y2 
TABULATE DIFFERENCE OF VARIANCE Y1 Y2 X 
. 
XTIC OFFSET 0.2 0.2 
X1LABEL GROUP ID 
Y1LABEL DIFFERENCE OF VARIANCE 
CHAR X 
LINE BLANK 
DIFFERENCE OF VARIANCE PLOT Y1 Y2 X 
CHAR X ALL 
LINE BLANK ALL 
BOOTSTRAP DIFFERENCE OF VARIANCE PLOT Y1 Y2 X  
    

Dataplot generated the following output.

       ********************************************
       **  LET A = DIFFERENCE OF VARIANCE Y1 Y2  **
       ********************************************
  
  
 THE COMPUTED VALUE OF THE CONSTANT A             =  0.49571407E+00
  
  
       ***********************************************
       **  TABULATE DIFFERENCE OF VARIANCE Y1 Y2 X  **
       ***********************************************
  
  
                 *    Y1       AND Y2
     X           *    DIFFERENCE OF VARIANCES
 **********************************************
     1.00000     *   -0.194408E-01
     2.00000     *    0.167963
     3.00000     *    0.300339
  
       GROUP-ID AND STATISTIC WRITTEN TO FILE DPST1F.DAT