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Message Posted: Fri, 09 Jan 2004 @ 21:34:33 GMT


     
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Subj:   Re: Sampling Method
 
From:   Victor Sokovin

Bill,

  We currently have an auditor using TD to select row samples. I have some "opinions" on the way sampling works, but no authoritative information. Given that we are currently on V2R3 and have no RANDOM function, does TD:  


  1. Move all rows into spool before selecting the sample?  


Not sure about the spool but at least in-memory.


  2. Use a.some internal random sampling algorithm or  


Yes.


  b.simply select each nth record given the whole population/sample size ratio to create the sample from the spool?  


Surely not. Just try the same query with the sample clause n times.


  3. Can anyone identify the "published" technique TD uses for sample selection by name or formula?  


I recall Geoffrey Rommel has explained this once on this forum and I have managed to look up the thread. Just search for the thread entitled "Random Sampling" in the Feb 2003 archive.


Regards,

Victor



     
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