DIFFERENCE OF TRIMMED MEAN

DIFFERENCE OF TRIMMED MEAN (LET)

Let Subcommand

Compute the difference between the trimmed means for two response variables.

The mean is the sum of the observations divided by the number of observations. The mean can be heavily influenced by extreme values in the tails of a variable. The trimmed mean compensates for this by dropping a certain percentage of values on the tails. For example, the 50% trimmed mean is the mean of the values between the upper and lower quartiles. The 90% trimmed mean is the mean of the values after truncating the lowest and highest 5% of the values.

For the differeence of trimmed means, the trimmed mean is computed for each of two samples then their difference is taken.

LET <par> = DIFFERENCE OF TRIMMED MEAN <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 trimmed means is stored;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.

LET A = DIFFERENCE OF TRIMMED MEAN Y1 Y2
LET A = DIFFERENCE OF TRIMMED MEAN Y1 Y2 SUBSET X > 1

The analyst must specify the percentages to trim in each tail. This is done by defining the internal variables P1 (the lower tail) and P2 (the upper tail). For example, to trim 10% off each tail, do the following:
LET P1 = 10
LET P2 = 10
LET A = DIFFERENCE OF TRIMMED MEAN Y1 Y2

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

None

None

TRIMMED MEAN	= Compute the trimmed mean.
DIFFERENCE OF MEDIAN	= Compute the difference of medians.
DIFFERENCE OF MEAN	= Compute the difference of means.
DIFFERENCE OF MIDMEAN	= Compute the difference of midmeans.
DIFFERENCE OF BIWEIGHT LOCATION	= Compute the difference of biweight locations.
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 P1 = 10 
LET P2 = 10 
LET A = DIFFERENCE OF TRIMMED MEAN Y1 Y2 
TABULATE DIFFERENCE OF TRIMMED MEAN Y1 Y2 X 
. 
XTIC OFFSET 0.2 0.2
X1LABEL GROUP ID
Y1LABEL DIFFERENCE OF TRIMMED MEANS
CHAR X 
LINE BLANK 
DIFFERENCE OF TRIMMED MEAN PLOT Y1 Y2 X 
CHAR X ALL 
LINE BLANK ALL 
BOOTSTRAP DIFFERENCE OF TRIMMED MEAN PLOT Y1 Y2 X  
    

Dataplot generated the following output.

       ************************************************
       **  LET A = DIFFERENCE OF TRIMMED MEAN Y1 Y2  **
       ************************************************
  
  
 THE COMPUTED VALUE OF THE CONSTANT A             =  0.27650001E+01
  
  
       ***************************************************
       **  TABULATE DIFFERENCE OF TRIMMED MEAN Y1 Y2 X  **
       ***************************************************
  
  
                 *    Y1       AND Y2
     X           *    DIFFERENCE OF TRIMMED MEANS
 **********************************************
     1.00000     *     1.58750
     2.00000     *     3.15750
     3.00000     *     3.61000
  
       GROUP-ID AND STATISTIC WRITTEN TO FILE DPST1F.DAT