Jennifer,
Please provide us more information. It would be helpful to see the
actual code you ran along with the actual output. How did you get the
values that your included with your email message? Did you get the
values using the summary function, e.g.
> fit0<-lm(y~x+sex+x*sex)
> summary(fit0)
Call:
lm(formula = y ~ x + sex + x * sex)
Residuals:
Min 1Q Median 3Q Max
-108.6049 -29.9293 -0.3111 27.8004 165.3499
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 8.62361 8.55021 1.009 0.314
x 3.88322 0.07252 53.548 <2e-16 ***
sex -11.78652 12.56677 -0.938 0.349
x:sex 1.22804 0.10882 11.285 <2e-16 ***
---
Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.?
0.1 ? ? 1
or some other way?
John
John David Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)>>>
Jennifer Hou <jennifer.hou at hotmail.de> 8/4/2010 4:22 PM >>>
Hello,
I have got a linear model that looks like this:
lm(criterion ~ variable.A*variable.a + variable.B*variable.b +
variable.C *variable.c)
The output computed with stdCoeff() seems to be all right, but it does
not show the coefficients of the interaction of the first pair of
variables. Instead, it shows "NA":
(Intercept)
NA
variable.A
0.0925094150
variable.a
0.1517246479
variable.B
-0.0023847092
variable.b
0.0256653197
variable.C
0.0194313471
variable.c
0.0192897539
variable.A : variable.a
NA
variable.B : variable.b
0.0471111439
variable.C : variable.c
0.0696702457
This happens with all my data frames, there is always a problem with
the first pair of variables. Does anyone have an idea why R does not
compute the coefficients of "variable.A : variable.a"?
Thanks in advance!
Best regards,
Jennifer
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