R help - Nov 2010 - SMATR common slopes test

Hi All,

I am confused with SMATR's test for common slope. My null hypothesis here is
that all slopes are parallel (common slopes?), right?
So if I get a p value < 0.05 means that we can have confidence to reject it?
That slopes are different?
Or the other way around? it means that we have statistical confidence that
the slopes are parallel?
thanks
-- 
Eugenio Larios
PhD Student
University of Arizona.
Ecology & Evolutionary Biology.
(520) 481-2263
elariosc@email.arizona.edu

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Eugenio -
> I am confused with SMATR's test for common slope. My null hypothesis
here is
> that all slopes are parallel (common slopes?), right?
> So if I get a p value < 0.05 means that we can have confidence to reject
it?
> That slopes are different?
> Or the other way around? it means that we have statistical confidence that
> the slopes are parallel?
Try this:

set.seed(5)
n <- 20
x <- rnorm(n)

y1 <- 2 * x + rnorm(n)
y2 <- 2 * x + rnorm(n)
y3 <- 4 * x + rnorm(n)

# Slopes approximately equal
slope.com(x = c(x, x), y = c(y1, y2), groups = rep(c(1,2), each = n))

#$p
#[1] 0.4498037

# Slopes of 2 and 4
slope.com(x = c(x, x), y = c(y1, y3), groups = rep(c(1,2), each = n))

#$p
#[1] 0.0003850332


Cheers,
Kevin

-------------------------------------------------
Kevin M. Middleton
Department of Biology
California State University San Bernardino