* This SPSS syntax file helps to explore the variances of the sum and
* difference of random variables.
*
* Last modified 09/10/03 by Tom Short.

* IMPORTANT -  COMPLETE THIS STEP BEFORE EXECUTING COMMANDS.

* First arrow down, press Enter, or Page Down to the row representing the number
* of observations you wish to generate.  Place a "." in the entry in the column and row 
* you wish to use.

* I used 50 observations for my example.

* Do this in each of the first two columns in the Data View window. 

* I used Transform > Random Number Seed... to set a seed of my choice.

SET SEED 18091003.

* I used Transform > Compute... to generate data from a Normal distribution. 

COMPUTE var00001 = RV.NORMAL(100,10) .
EXECUTE .

* I used Transform > Compute... to generate some more Normal data.

COMPUTE var00002 = RV.NORMAL(50,5) .
EXECUTE .

* I used Transform > Compute... again to find the sum and difference.

COMPUTE sum = var00001+var00002 .
EXECUTE .

COMPUTE diff = var00001-var00002 .
EXECUTE .

* I chose Analyze > Descriptive Statistics > Descriptives... to explore the
* means, standard deviations, and variances of the variables.

DESCRIPTIVES
  VARIABLES=var00001 var00002 sum diff
  /STATISTICS=MEAN STDDEV VARIANCE .

* END.