[R] Find if there is independence

[kjetil halvorsen]

Or you can use chisq.test with simulate.p.value=TRUE

Kjetil Halvorsen


Uwe Ligges wrote:
> 
> Ambrosini Alessandro wrote:
> >
> > Hello
> > I have the matrix
> >
> > a<-matrix(c(2,1,0,1,2,2,1,5,7,2,5,12),nrow=6)
> > a
> >
> >       [,1] [,2]
> > [1,]    2    1
> > [2,]    1    5
> > [3,]    0    7
> > [4,]    1    2
> > [5,]    2    5
> > [6,]    2   12
> >
> > Suppose that in the first row we have 3 men of England, 2 with hair, and 1
> > no
> > In the second we have 6 italian men, 1 with hair and 5 no ...
> > I want to find if there is a dependence between men withouth hair and
> > nationality.
> > By the way, which is the simplest command to use to study the independence
> > in a matrix like the one that I wrote?
> 
> Let me ask another question: What is the appropriate method to ...
> 
> Since the cells of your contingency table are not very well filled, I'd
> suggest to use Fisher's (general) exact test, if you want to test on
> independency of rows and columns, fortunately you do not need to
> calculate it manually, see ?fisher.test .
> 
> > Using
> > > chisq.test(a)
> >
> >         Pearson's Chi-squared test with Yates' continuity correction
> >
> > data:  a
> > X-squared = 0, df = 1, p-value = 1
> 
> No. In my version of R (1.5.0 on WinNT) it results plausibly in:
>   X-squared = 6.8155, df = 5, p-value = 0.2347
> 
> Are you sure you did the things mentioned above exactly?
> 
> > Warning message:
> > Chi-squared approximation may be incorrect in: chisq.test(a)
> >
> > Why does it give me the warning message? What have to add into chisq.test(a)
> > ?
> > And in which value I can understand the level of the dependence?
> 
> What does "level of dependence" mean in your case?
> Are you sure you want to quantify it, using such a small number of
> observations and such vague defintions (hair / no hair). To you want to
> quantify it for all countries or separately? But perhaps I misunderstand
> ...
> 
> Uwe Ligges
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