newbie problem using Design.rcs
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? 2) f <- ols(y ~ rcs(x,3), data=mydata) Function(f) does not produce anything for me (i.e.) it's empty. Sincerely, sp
--- On Tue, 12/23/08, Frank E Harrell Jr <f.harrell at vanderbilt.edu> wrote:
From: Frank E Harrell Jr <f.harrell at vanderbilt.edu> Subject: Re: [R] newbie problem using Design.rcs To: to_rent_2000 at yahoo.com Cc: "David Winsemius" <dwinsemius at comcast.net>, r-help at 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