sp wrote:
Dr. Harrell,
Thanks for your patient replies. I've two more questions:
1) Is your book appropriate for beginners or is it more for advanced users?
It is in the middle of those two.
2) f <- ols(y ~ rcs(x,3), data=mydata)
Function(f)
does not produce anything for me (i.e.) it's empty.
Here's a test I just ran
> y <- rnorm(100)
> x <- runif(100)
> f <- ols(y ~ rcs(x,3))
> Function(f)
function(x = NA) {-0.18307779+0.91343138*
x-2.1908543*pmax(x-0.10568075,0)^3+3.8312836*pmax(x-0.45620427,0)^3-1.6404293*pmax(x-0.92434146,0)^3
}
<environment: 0x2ca30a8>
If you are doing this inside { } you will need to do print(Function(f))
Note this is a simplified version of the rcs with 2 redundant terms to
avoid writing in terms of differences in cubes.
Frank
Sincerely,
sp
--- On Tue, 12/23/08, Frank E Harrell Jr <f.harr...@vanderbilt.edu> wrote:
From: Frank E Harrell Jr <f.harr...@vanderbilt.edu>
Subject: Re: [R] newbie problem using Design.rcs
To: to_rent_2...@yahoo.com
Cc: "David Winsemius" <dwinsem...@comcast.net>, r-help@r-project.org
Date: Tuesday, December 23, 2008, 4:57 PM
sp wrote:
2. I didn't have x^3 b/c that co-efficient happens
to be zero in this fitting.
That's strange.
Also, I'm forced to call win.graph() before my
first plot() to see the first plot. Is that normal?
no
I started with testing it on just x,y dimensions so
that I can visually evaluate the fitting. I tried y=x, y=x^2
etc, adding Gaussian noise each time (to the y).
I plot original x,y and x,y' where y' is
calculated using the co-efficients returned by rcs. I find
that the regression curve differs from the actual points by
as high as 10^5 with 3 knots and roughly -10^5 with 4 knots
as I make y=x^2, y=x^3....
wait until you have studied regression
Frank
If this is NOT a good way to test fitting, could you
pls tell me a better way?
Respectfully,
sp
--
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
