 Dataplot Vol 2 Vol 1

# DIFFERENCE OF VARIANCE

Name:
DIFFERENCE OF VARIANCE (LET)
Type:
Let Subcommand
Purpose:
Compute the difference between the variances for two response variables.
Description:
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.

Syntax:
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.
Examples:
LET A = DIFFERENCE OF VARIANCE Y1 Y2
LET A = DIFFERENCE OF VARIANCE Y1 Y2 SUBSET X > 1
Note:
Dataplot statistics can be used in a number of commands. For details, enter

Default:
None
Synonyms:
None
Related Commands:
 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.
Applications:
Data Analysis
Implementation Date:
2003/03
Program:
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 NIST is an agency of the U.S. Commerce Department.

Date created: 03/27/2003
Last updated: 11/12/2015