Chi -square test

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Chi -square test

ganesh
Dear all,

I have 800 sample size and the contingency table forms 3 * 11. I am doing SPSS Chi square test statistics . Pearson chi-square test shows the results is significant . But at the bottom it  shows  33.3% have expected count less than 5 and minimum expected count is .63. The table does have results of fisher exact test ? what should i do ?
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Re: Chi -square test

Bruce Weaver
Administrator
First a note on terminology.  Fisher's exact test (sometimes called the Fisher-Irwin test, because Irwin developed the same test independently of Fisher) is for 2x2 tables.  What you're getting for a 3x11 table is an extension (of some sort) of the FET.  Personally, I wish SPSS would not call it FET.  

Eleven is a lot of categories.  What are the two variables?  Are they purely nominal, or are the categories
ordered?  Can any categories be combined in a meaningful way?


ganesh wrote
Dear all,

I have 800 sample size and the contingency table forms 3 * 11. I am doing SPSS Chi square test statistics . Pearson chi-square test shows the results is significant . But at the bottom it  shows  33.3% have expected count less than 5 and minimum expected count is .63. The table does have results of fisher exact test ? what should i do ?
--
Bruce Weaver
bweaver@lakeheadu.ca
http://sites.google.com/a/lakeheadu.ca/bweaver/

"When all else fails, RTFM."

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Re: Chi -square test

Rich Ulrich
In reply to this post by ganesh
Well, what did the Exact Test (don't call it Fisher's) say?  Was it significant, too,
and to a similar p-level?  - In that case, you might merely add, "Although some
Expected cell frequencies were small, the overall p-level was  also < ...?> by
an Exact Test."

Personally, I always tried to avoid having as many as 11 categories,
because it is hard to discuss that many, and there are hardly ever so
many that are actually interesting, especially when you consider some
small observed Ns for the lesser categories.  - You can lump small
numbers into "Other (too small for testing)" if that description fits the
case.  Or, as Bruce W. suggests already, sometimes it is possible to
test a more precise hypothesis, with fewer degrees of freedom (and
thus, more power) by considering whether the categories are ordered,
or if there is some other principle for a better test.

By the way, the particular *problem* with the X^2 approximation when
Expected-frequencies are small is that a tiny value, as a divisor, may inflate the
contribution of cell unreasonably.  You might look at the contributions cell-by-
cell to confirm that this has not happened to your data.

--
Rich Ulrich

> Date: Wed, 21 Sep 2011 01:42:26 -0700

> From: [hidden email]
> Subject: Chi -square test
> To: [hidden email]
>
> Dear all,
>
> I have 800 sample size and the contingency table forms 3 * 11. I am doing
> SPSS Chi square test statistics . Pearson chi-square test shows the results
> is significant . But at the bottom it shows 33.3% have expected count less
> than 5 and minimum expected count is .63. The table does have results of
> fisher exact test ? what should i do ?
>
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Re: Chi -square test

Ryan
In reply to this post by ganesh
You need to give us more--study design, variables, research questions, etc.

Ryan

On Wed, Sep 21, 2011 at 4:42 AM, ganesh <[hidden email]> wrote:

> Dear all,
>
> I have 800 sample size and the contingency table forms 3 * 11. I am doing
> SPSS Chi square test statistics . Pearson chi-square test shows the results
> is significant . But at the bottom it  shows  33.3% have expected count less
> than 5 and minimum expected count is .63. The table does have results of
> fisher exact test ? what should i do ?
>
> --
> View this message in context: http://spssx-discussion.1045642.n5.nabble.com/Chi-square-test-tp4825612p4825612.html
> Sent from the SPSSX Discussion mailing list archive at Nabble.com.
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