Partial correlations and p-values

Awesome, that's what I was looking for. ?I have two additional questions: (1)
What can I do if the variables are of different lengths? (2) How do I update
the formula if I want to control for more than one variable.

Let's take the following example:
x <- c(1,20,14,7,9)
y <- c(5,6,7,9,10,11)
z <- c(13,27,16,5,4,17,20)
a <- c(4,6,7,1)

xres <- residuals(lm(x ~ z))
yres <- residuals(lm(y ~ z))
cor(xres, yres)
ct <- cor.test(xres, yres)
ct$estimate
ct$p.value

How do I update the above formula to:
(1) take into account that the variables are of different lengths? ?I get an
error when calculating the residuals.
(2) control for z and a (i.e., more than one variable)?

Thanks so much for your help.


Peter Ehlers wrote:

dadrivr wrote:

I'm trying to write code to calculate partial correlations (along with
p-values). ?I'm new to R, and I don't know how to do this. ?I have
searched
and come across different functions, but I haven't been able to get any
of
them to work (for example, pcor and pcor.test from the ggm package).

In the following example, I am trying to compute the correlation between
x
and y, while controlling for z (partial correlation):

x <- c(1,20,14,7,9)
y <- c(5,6,7,9,10)
z <- c(13,27,16,5,4)

What function can I append to this to find this partial correlation?
Many
thanks!

I'm not sure what you need, but does this give you what
you want:

xres <- residuals(lm(x ~ z))
yres <- residuals(lm(y ~ z))
cor(xres, yres)
# [1] 0.9778857

or

ct <- cor.test(xres, yres)
ct$estimate ?# 0.9978857
ct$p.value ? # 0.003934582

? -Peter Ehlers

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