[R] R help contingency table

[Jim Lemon]

Hi Lucie,
You can visualize this using the sizetree function (plotrix). You
supply a data frame of the individual choice sequences.

# form a data frame of "random" choices
coltrans<-data.frame(choice1=sample(c("High","Medium","Low"),100,TRUE),
 choice2=sample(c("High","Medium","Low"),100,TRUE))
sizetree(coltrans,main="Random color choice transitions")
# test the two way table of transitions for independence
chisq.test(table(coltrans))
# now try a data frame of "habitual" choices
coltrans2<-data.frame(choice1=rep(c("High","Medium","Low"),c(33,33,34)),
 choice2=c(sample(c("High","Medium","Low"),33,TRUE,prob=c(0.6,0.2,0.2)),
 sample(c("High","Medium","Low"),33,TRUE,prob=c(0.2,0.6,0.2)),
 sample(c("High","Medium","Low"),34,TRUE,prob=c(0.2,0.2,0.6))))
sizetree(coltrans2,main="Habitual color choice transitions")
# test the table again
chisq.test(table(coltrans2))

This may be what you want.

Jim


On Mon, Jun 20, 2016 at 12:09 PM, Lucie Dupond <loupiote93 at hotmail.fr> wrote:
> Hello,
> I'm sorry if my question is really basic, but I'm having some troubles with the statistics for my thesis, and especially the khi square test and contingency tables.
>
> For what I understood, there are two "kinds" of khisquare test, that are quite similar :
> - Homogeneity, when we have one variable and we want to compare it with a theorical distribution
> - Independence test, when we have 2 variable and we want to see if they are linked
>
> -- -
>
> I'm working on color transitions, with 3 possible factors : « High » , « Medium » and « Low »
> I want to know if an individual will go preferably from a color « High » to another color « High », more than from a color « High » to a color « Medium » (for example)
>
> I have this table :
>
> trans1<-c(51,17,27,12,21,13,37,15,60)
> transitions1<-matrix(trans1, nrow=3, ncol=3, byrow=T)
> rownames(transitions1) <- c("High"," Medium", "Low")
> colnames(transitions1) <- c("High"," Medium", "Low")
>
> The first colomn is showing the first color, and the second is showing the second color of the transition
>
> It looks like I'm in the case of an Independence test, in order to see if the variable "second color" is linked to the "first color".
>
> So I'm making the test :
>
> chisq.test(transitions1)
>
>
> (If I understood well, the test on the matrix is the independence  test, and the test on the vector trans1 is the homogeneity test ?)
>
> The result is significatif, it means that some transitions are prefered.
>
> My problem is that I have other transition tables like this one (with other individuals or other conditions)
> For example, I also have this one :
>
>
> trans2<-c(13,7,8,5,16,18,11,8,17)
> transitions2<-matrix(trans2, nrow=3, ncol=3, byrow=T)
> rownames(transitions2) <- c("High","Low", "Stick")
> colnames(transitions2) <- c("High","Low", "Stick")
>
> I want to know if the "prefered" transitions in the table 1 are the same in the table 2.
> But if I try a khisquare test on those two matrix, R only takes the first one.
>
> How can I compare those tables
> Maybe with another test ?
>
> Thanks in advance !
>
> Kind regards
>
> Lucie S.
>
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>
>
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