"Kum-Hoe Hwang" <phdhwang at gmail.com> writes:
> Howdy Gurus !
>
> I have a different correlation result from the same data. The
> "corridor1" string variable is expressed
> as a number like the "corridor2" number variable.
> --------------------------------------------------------------------------
> > levels(corridor1)
> [1] "A" "B" "C" "D"
"E" "F"
> > levels(as.factor(corridor2))
> [1] "0" "1" "2" "3" "4"
> >
>
------------------------------------------------------------------------------------------
> I have the correlation results followings using cor() function.
>
------------------------------------------------------------------------------------------
> > cor(jh1_1, as.factor(corridor1))
> [1] 0.01528538
> > cor(jh1_1, as.factor(corridor2))
> [1] -0.4972571
>
------------------------------------------------------------------------------------------
> I donot know why the above correlation coefficients used the same data
> are different.
> They are 0.015 from as.factor(corridor1), -0.497 from as,factor(corridor2).
> The string variable "corridor1" is the same catergory data with
the
> variable corridor2.
> The difference is that "A" is replaced with "0",
"B" with "1", "C"
> with "2", .....
>
> Could you tell me why they are different, and which correlation
> coefficient is correct?
One thing that strikes me is that corridor1 has 6 levels and corridor2
has 5...
In general correlations are not expected to work on factors so I'd be
explicit about taking as.numeric(). A glance at
table(corridor1,corridor2) should be informative too, as would a
summary(as.numeric(as.factor(corridor1))-as.numeric(as.factor(corridor1)))
--
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