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PSPP-BUG: [bug #35420] Regression output round off problem

From: anonymous
Subject: PSPP-BUG: [bug #35420] Regression output round off problem
Date: Tue, 31 Jan 2012 22:31:52 +0000
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20110420 Firefox/3.6.17 (.NET CLR 3.5.30729)


                 Summary: Regression output round off problem
                 Project: PSPP
            Submitted by: None
            Submitted on: Tue 31 Jan 2012 10:31:51 PM UTC
                Category: Numerical Errors
                Severity: 5 - Average
                  Status: None
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                 Release: None
                  Effort: 0.00



  I was experimenting with the correlation and regression features using the
physiology.sav file from the example folder. I noticed that the residual for
the variable "weight" for case 38 was very large. I then noticed that the
weight for this case was apparently incorrect - it was negative.

  I deleted the negative sign and ran the analysis again to see how much it
improved.  I was alarmed to see that the second run produced a multiple R of
1.00.  Although the predictions improved, they are clearly not perfect.

  I ran the analysis in SPSS, and found that the R was .998 - which would
round up to 1.00 (and the R square of .996 would also round up to 1.00). 
Although 1.00 is technically correct, to two significant digits, I think that
it's worth changing the output in cases like this - or printing a warning.

  I have included the modified .sav file.  RES1 and PRED1 were produced BEFORE
I corrected the negative weight.  RES2 and PRED2 were produced with the
modified file.  I have also included a pdf of the output file - the second run
of the regression procedure was with the modified data file and shows the R of


File Attachments:

Date: Tue 31 Jan 2012 10:31:51 PM UTC  Name: physiologyCorrected.sav  Size:
3kB   By: None

Date: Tue 31 Jan 2012 10:31:51 PM UTC  Name: physiologyCorrectedOutput.pdf 
Size: 35kB   By: None



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