On Sat, 8 Aug 2009, Katharina May wrote:
Thanks to somebody I got the hint to use offset for the purpose of
validating if there's
a difference between the intercept and slope of a model and some
provided values for
the coefficients intercept and slope.
You could also use a Wald test for a linear hypothesis which does not
require refitting of the data under the null hypothesis. Suppose you've
got the regression
fm <- lm(dist ~ speed, data = cars)
and then want to test the null hypothesis that
(Intercept) = -10
speed = 4
Then you can do
library("car")
linear.hypothesis(fm, c("(Intercept) = -10", "speed = 4"))
which will give you an ANOVA-like output.
Conceptually, this approach should also be possible for models with random
effects but I don't think that linear.hypothesis() works out of the box
for this.
Z
I read ?model.offset and I'm still struggling to use it for my
purpose. If I understood
the concepts correctly, offset can be used to define a known
coefficient of a model,
so therefore I could create two models based on the same data like my
original one
with an additional offset term (one model with intercept specified
and one with the
slope specified)?
Sorry for troubling you: I struggling with the data analysis of my
bachelor thesis and
just want to compare the coefficients of my linear regression to
published ones...
a method often used I guess, but still I cannot find any appropriate
documentations.
Thanks,
Katharina
On Aug 8, 2009, Katharina May <may.kathar...@googlemail.com> wrote:
Hi there,
I've got a question which is really trivial for sure but still I have
to ask as I'm not
making any progress solving it by myself (please be patient with an
undergraduate
student):
I've got a linear model (lm and lmer fitted with method="ML").
Now I want to compare the coefficients (slope, intercept, not the
random effects)
of both models with a given value (e.g. intercept=0.5, slope=2) to see
if the values
estimated with the models are significantly different from the given values.
I heard about t.test, but I'm sorry to say that I'm not quite
understanding what I have
to provide as arguments.
I would be more than happy if somebody can point out an example similar to
the
comparison I have to do...
Thanks,
Katharina
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