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Status Not under consideration
Workspace SPSS Statistics
Created by Guest
Created on Dec 18, 2019

Setting Seeds

I want to do model testing while always drawing the same training data with the help of a random variable (e.g. command NAIVEBAYES). It is important to always produce the same numbers. In SPSS I can do it with SET but there are pitfalls the user might not be aware of:

 

* Method 1a (Variables produce different values).
SET RNG=MT MTINDEX=2019.
COMPUTE Test1a = RV.NORMAL(100,10).
COMPUTE Test2a = RV.NORMAL(100,10).
COMPUTE Test3a = RV.NORMAL(100,10).
EXECUTE.

* Method 1b (works like Method 1a; 2nd and 3rd SET commands are being ignored).
SET RNG=MT MTINDEX=2019.
COMPUTE Test1b = RV.NORMAL(100,10).
SET RNG=MT MTINDEX=2019.
COMPUTE Test2b = RV.NORMAL(100,10).
SET RNG=MT MTINDEX=2019.
COMPUTE Test3b = RV.NORMAL(100,10).
EXECUTE.

* Method 2 (variables produce exactly the same values).
SET RNG=MT MTINDEX=2019.
COMPUTE Test4 = RV.NORMAL(100,10).
EXECUTE.
SET RNG=MT MTINDEX=2019.
COMPUTE Test5 = RV.NORMAL(100,10).
EXECUTE.
SET RNG=MT MTINDEX=2019.
COMPUTE Test6 = RV.NORMAL(100,10).
EXECUTE.

* Method 3 (variables are transposes of test1b to test3b).
SET RNG=MT MTINDEX=2019.
COMPUTE TestVar7 = RV.NORMAL(100,10).
EXECUTE.
COMPUTE TestVar8 = RV.NORMAL(100,10).
EXECUTE.
COMPUTE TestVar9 = RV.NORMAL(100,10).
EXECUTE.

 

It seems like this is one of those rare examples where an immediate EXECUTE is needed.

Needed by Date Dec 18, 2019