DIFFERENCE OF RELATIVE SD

DIFFERENCE OF RELATIVE SD (LET)

Let Subcommand

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

The relative standard deviation is:
\( \mbox{relsd} = \frac{100 s}{|\bar{x}|} \)

with s and \( \bar{x} \) denoting the standard deviation and mean, respectively.

Some analysts prefer to call this the percent relative standard deviation and the value obtained without multiplying by 100 the relative standard deviation. If this is your preference, simply divide the obtained value by 100 with the LET command. This differs from the coefficient of variation in that the absolute value of the mean is taken and the value is expressed as a percentage.

For the difference of relative standard deviations, the relative standard deviation is computed for each of two samples then their difference is taken.

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

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

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

None

DIFFERENCE OF RELATIVE STANDARD DEVIATION is a synonym for DIFFERENCE OF RELATIVE SD.

RELATIVE SD	= Compute the relative sd.
RELATIVE VARIANCE	= Compute the relative variance.
COEFFICIENT OF VARIATION	= Compute the coefficient of variation.
STANDARD DEVIATION	= Compute the standard deviation.
DIFFERENCE OF RELATIVE VARIANCE	= Compute the difference of the relative variances.
DIFFERENCE OF COEFFICIENT OF VARIATION	= Compute the difference of the coefficient of variation.
DIFFERENCE OF SD	= Compute the difference of standard deviations.
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 RELATIVE SD Y1 Y2 
TABULATE DIFFERENCE OF RELATIVE SD Y1 Y2 X 
. 
XTIC OFFSET 0.2 0.2 
X1LABEL GROUP ID 
Y1LABEL DIFFERENCE OF RELATIVE SD 
CHAR X 
LINE BLANK 
DIFFERENCE OF RELATIVE SD PLOT Y1 Y2 X 
CHAR X ALL 
LINE BLANK ALL 
BOOTSTRAP DIFFERENCE OF RELATIVE SD PLOT Y1 Y2 X  
    

Dataplot generated the following output.

       ***********************************************
       **  LET A = DIFFERENCE OF RELATIVE SD Y1 Y2  **
       ***********************************************
  
  
 THE COMPUTED VALUE OF THE CONSTANT A             = -0.85294724E-01
  
  
       **************************************************
       **  TABULATE DIFFERENCE OF RELATIVE SD Y1 Y2 X  **
       **************************************************
  
  
                 *    Y1       AND Y2
     X           *    DIFFERENCE OF RELATIVE SD
 **********************************************
     1.00000     *    -4.01654
     2.00000     *    -2.63285
     3.00000     *    -1.19178
  
       GROUP-ID AND STATISTIC WRITTEN TO FILE DPST1F.DAT