Thanks everyone,
for your prompt answers to such an elementary question. I finally got
my head wrapped around this by making a table with dummy data,
creating contrasts by hand, and plotting both the raw data and the
contrasts. It all makes sense now. :)
Gernot
On May 8, 2009, at 12:23 P
This is also covered in the following paper (and others):
Garland, T., Jr., P. H. Harvey, and A. R. Ives. 1992. Procedures for the
analysis of comparative data using phylogenetically independent contrasts.
Systematic Biology 41:18-32.
Available here:
http://www.biology.ucr.edu/people/fa
Gernot Huber asked --
> 1. Why do you have to force a linear regression through the origin
> when using phylogenetically independent contrasts (PICs)?
Because their expectations are zero. A contrast could be either
X1 - X2 or X2 - X1, for one thing. The expectations of X1 and X2
are identica
Hi,
I haven't been able to find answers to the following questions:
1. Why do you have to force a linear regression through the origin
when using phylogenetically independent contrasts (PICs)?
2. If you suspect an inverse linear relationship, would you transform
one axis so you could still
