[R] In chisq.test(x) : Chi-squared approximation may be incorrect

[Simon Blomberg]

Why do people automatically jump to Fisher's Exact test? That test
conditions on BOTH marginal row totals. Usual contingency table analyses
condition on one margin, at most. You should look very carefully at the
underlying model for your data. Fisher's Exact test might not be
appropriate. Agresti's "Categorical Data Analysis" has a good discussion
of this.

Simon.

On Tue, 2008-01-15 at 21:49 -0500, My Coyne wrote:
> Thank you for your help; I will try fisher.test().
> 
>  
> 
> 
> 
> From: anna freni sterrantino [mailto:annafreni at yahoo.it] 
> Sent: Tuesday, January 15, 2008 8:53 PM
> To: mcoyne at boninc.com; r-help at stat.math.ethz.ch
> Subject: Re: [R] In chisq.test(x) : Chi-squared approximation may be incorrect
> 
>  
> 
> Hi!
>  the warning you got
> "Chi-squared approximation may be incorrect"
> is because probably there are less than 5 observations in
> the cell. Maybe will help to 
> try fisher.test()
> 
> Cheers
> 
> Anna
> 
> 
> 
> 
> 
> 
> 
> 
> ----- Messaggio originale -----
> Da: My Coyne <mcoyne at boninc.com>
> A: r-help at stat.math.ethz.ch
> Inviato: Lunedì 14 gennaio 2008, 21:51:30
> Oggetto: [R] In chisq.test(x) : Chi-squared approximation may be incorrect
> 
> Hello,
> 
> 
> 
> I received the following warning when running chi-square;
> 
> n  Is there a way to catch the 'error' code of 'warning' after run
> chisq.test(x)?
> 
> n  What does this error mean?
> 
> 
> 
> Thank you for your help.
> 
> 
> 
> 
> 
> 
>     [[alternative HTML version deleted]]
> 
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-- 
Simon Blomberg, BSc (Hons), PhD, MAppStat. 
Lecturer and Consultant Statistician 
Faculty of Biological and Chemical Sciences 
The University of Queensland 
St. Lucia Queensland 4072 
Australia
Room 320 Goddard Building (8)
T: +61 7 3365 2506
http://www.uq.edu.au/~uqsblomb
email: S.Blomberg1_at_uq.edu.au

Policies:
1.  I will NOT analyse your data for you.
2.  Your deadline is your problem.

The combination of some data and an aching desire for 
an answer does not ensure that a reasonable answer can 
be extracted from a given body of data. - John Tukey.