[R] testing independence of categorical variables

[Ramin Shamshiri]

The chi-square does not need your two categorical variables to have equal
levels, nor limitation for the number of levels.

The Chi-square procedure is as follow:
χ^2=∑_(All Cells)▒〖(Observed-Expected)〗^2/Expected

Expected Cell= E_ij=n((i^th RowTotal)/n)((j^th RowTotal)/n)

Degree of Freedom=df= (row-1)(Col-1)

This way should not give you any errors if your calculations are all
correct. I usually use SAS for calculations like this. Below is a sample
code I wrote to test whether US_State and Blood type are independent. You
can modify it for your data and should give you no error.

data bloodtype;
input bloodtype$ state$ count@@;
datalines;
A FL 122 B FL 117
AB FL 19 O FL 244
A IA 1781 B IA 351
AB IA 289 O IA 3301
A MO 353 B MO 269
AB MO 60 O MO 713
;
proc freq data=bloodtype;
tables bloodtype*state
/ cellchi2 chisq expected norow nocol nopercent;
weight count;
quit;


Best
Ramin
Gainesville



Shoaaib Mehmood wrote:
> 
> hi,
> 
> is there a way of calculating of measuring dependence between two
> categorical variables. i tried using the chi square test to test for
> independence but i got error saying that the lengths of the two
> vectors don't match. Suppose X and Y are two factors. X has 5 levels
> and Y has 7 levels. This is what i tried doing
> 
>>temp<-chisq.test(x,y)
> 
> but got error "the lengths of the two vectors don't match". any help
> will be appreciated
> -- 
> Regards,
> Rana Shoaaib Mehmood
> 
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