Re: exact versus asymptotic p-value under normal circumstances

Posted by Bruce Weaver on
URL: http://spssx-discussion.165.s1.nabble.com/Revision-control-for-SPSS-source-code-tp4267835p4273911.html

Sorry Tony, but I'm about to throw a spanner into the works.  One of my colleagues just started using v19, and it is not yet patched, so I asked him to run the code.  He got the same p-values I did for the two exact tests.

Exact p = .216 for Pearson
Exact p = .219 for Likelihood ratio

Cheers,
Bruce


Anthony Babinec wrote
Bruce,
Good work. Your reported results make sense. A quick run in unpatched
version 19
shows results that do not agree and could be suspect. Those are the numbers
that are being reported by Bridgette. I don't have StatXact on
the machine where I'm at, but would think that its results would agree with
the ones your report. So, this appears to be a problem -- known or unknown
-- in
version 19.


Tony Babinec
[hidden email]

-----Original Message-----
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of
Bruce Weaver
Sent: Thursday, March 31, 2011 10:08 AM
To: [hidden email]
Subject: Re: exact versus asymptotic p-value under normal circumstances

I just discovered that Bridgette sent some output to the Hotmail account I
use for posting to this list.  (Bridgette, as it says in my sig file, I only
use that account for mailing to this list, and check it only occasionally.
If you want to correspond off-list, please use the everyday e-mail address
given in my sig file.)

So, here is syntax to generate her table, and the tests of interest.  Notice
that the results I get do not match the ones she sent me.

* Bridgette's data.
data list list / row col kount (3f5.0).
begin data
1 1 11
1 2 16
2 1 14
2 2 35
3 1 8
3 2 21
4 1 23
4 2 27
end data.

var lab
 row "Death personality"
 col "Age group"
.
val lab
 row 1 "Cruel"
     2 "Gentle"
     3 "Impassive"
     4 "Other/variable" /
 col 1 "Under 40"
     2 "40 plus"
.
weight by kount .
crosstabs row by col / stat = chisqr.

* For those who have the Exact Tests module .

CROSSTABS
  /TABLES=row BY col / stat = chisqr
  /METHOD=EXACT TIMER(5).

* My results (using v18 with all patches under Windoze XP Professional):
* Pearson:  Asymptotic p = .213, exact p = .216 .
* Likelihood ratio:  Asymptotic p = .212, exact p = .219 .

* Output Bridgette sent me:
* Pearson:  Asymptotic p = .213, exact p = .028 .
* Likelihood ratio:  Asymptotic p = .212, exact p = .047 .


Bridgette, what version of SPSS are you using?  Have all the available
patches been applied?

Also, regarding Age Group, why group?  Do you have the actual ages?

Cheers,
Bruce

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Bruce Weaver
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http://sites.google.com/a/lakeheadu.ca/bweaver/

"When all else fails, RTFM."

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