[R] Phi coefficient matrix (package psych)

[William Revelle]

> 
> Kumar and Jim,
>  The phi coefficient is identical to the Pearson coefficient in the case of a 2 x 2 data set.
> 
> As it says in the help file for phi:
> 
> "Since the phi coefficient is just a Pearson correlation applied to dichotomous data, to find a matrix of phis from a data set involves just finding the correlations using cor or lowerCor or corr.test.”
> 
> So,  you can do a cor(df)  and you do not need the phi(df)
> 
> If you want the tetrachoric (which estimates what a Pearson would be if you had not artificially dichotomized the data) try tetrachoric(df)
> 
> Bill
> 


> 
> 
> 
>> On Apr 21, 2015, at 3:34 PM, Kumar Mainali <kpmainali at gmail.com> wrote:
>> 
>> I want to calculate phi coefficient for every pair of the columns. Is there
>> a way to generate a matrix like a correlation matrix? I know cor function
>> in the case below gives same answer as phi coefficient.
>> 
>> ​x <- sample(c(0,1), 10, replace=TRUE)
>> y <- sample(c(0,1), 10, replace=TRUE)
>> z <- sample(c(0,1), 10, replace=TRUE)
>> df <- data.frame(x,y,z)
>> cor(df)
>> library(psych)
>> phi(df)​
>> 
>> Thank you,
>> Kumar Mainali
>> Postdoctoral Associate
>> Department of Biology
>> University of Maryland
>> ᐧ
>> 
>> 	[[alternative HTML version deleted]]
>> 
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> 
> William Revelle		           http://personality-project.org/revelle.html
> Professor			           http://personality-project.org
> Department of Psychology   http://www.wcas.northwestern.edu/psych/
> Northwestern University	   http://www.northwestern.edu/
> Use R for psychology             http://personality-project.org/r
> It is 3 minutes to midnight	   http://www.thebulletin.org
> 
> 
> 
> 
> 
> 

William Revelle		           http://personality-project.org/revelle.html
Professor			           http://personality-project.org
Department of Psychology   http://www.wcas.northwestern.edu/psych/
Northwestern University	   http://www.northwestern.edu/
Use R for psychology             http://personality-project.org/r
It is 3 minutes to midnight	   http://www.thebulletin.org