DIFFERENCE OF SD

DIFFERENCE OF SD (LET)

Let Subcommand

Compute the difference between the standard deviations for two response variables.

The standard deviation is a common measure of the spread of a distribution or variable. The formula is:
\( s = \sqrt{\frac{\sum_{i=1}^{n}{(x - \bar{x})^2}}{n-1}} \)
For the difference of standard deviations, the standard deviation is computed for each of two samples then their difference is taken.

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

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

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

None

None

STANDARD DEVIATION	= Compute the standard deviation.
MEAN	= Compute the mean.
DIFFERENCE OF MEAN	= Compute the difference of the means.
DIFFERENCE OF MAD	= Compute the difference of the mad.
DIFFERENCE OF AAD	= Compute the difference of the aad.
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 SD Y1 Y2 
TABULATE DIFFERENCE OF SD Y1 Y2 X 
. 
XTIC OFFSET 0.2 0.2 
X1LABEL GROUP ID 
Y1LABEL DIFFERENCE OF SD 
CHAR X 
LINE BLANK 
DIFFERENCE OF SD PLOT Y1 Y2 X 
CHAR X ALL 
LINE BLANK ALL 
BOOTSTRAP DIFFERENCE OF SD PLOT Y1 Y2 X  
    

Dataplot generated the following output.

       **************************************
       **  LET A = DIFFERENCE OF SD Y1 Y2  **
       **************************************
  
  
 THE COMPUTED VALUE OF THE CONSTANT A             =  0.39219981E+00
  
  
       *****************************************
       **  TABULATE DIFFERENCE OF SD Y1 Y2 X  **
       *****************************************
  
  
                 *    Y1       AND Y2
     X           *    DIFFERENCE OF STANDARD DEVIATI
 **********************************************
     1.00000     *   -0.265747E-01
     2.00000     *    0.202373
     3.00000     *    0.313383
  
       GROUP-ID AND STATISTIC WRITTEN TO FILE DPST1F.DAT