R help - Nov 2006 - Forcing the intercept

Dear R-users:

I am doing multiple regressions using the "lm" function and would like
to
force the intercept to be equal to a specific value (such as 4.3).  I was
able to find out how to force it through the origin but this does not work
for other values. 

I am also interested in forcing the regression parameters obtained from one
regression in another regression with a subset of the data.

Are either of these possible in R?  I have been searching the help guide for
hours and have been unsuccessful.

Many thanks,
Heather

you can just subtract 4.3 from the independent variable and then do
through zero. That will
Give you a force through 4.3. I don't undersarand the second part of
your statement.



-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Heather Maughan
Sent: Monday, November 13, 2006 6:31 PM
To: r-help at stat.math.ethz.ch
Subject: [R] Forcing the intercept

Dear R-users:

I am doing multiple regressions using the "lm" function and would like
to force the intercept to be equal to a specific value (such as 4.3).  I
was able to find out how to force it through the origin but this does
not work for other values. 

I am also interested in forcing the regression parameters obtained from
one regression in another regression with a subset of the data.

Are either of these possible in R?  I have been searching the help guide
for hours and have been unsuccessful.

Many thanks,
Heather

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On Mon, 13 Nov 2006, Heather Maughan wrote:
> Dear R-users:
>
> I am doing multiple regressions using the "lm" function and would
like to
> force the intercept to be equal to a specific value (such as 4.3).  I was
> able to find out how to force it through the origin but this does not work
> for other values.
?offset, e.g  0+x1+x2+offset(rep(4.3, 127))

You could also use y-4.3 ~ rhs, but that gives problems for prediction.
> I am also interested in forcing the regression parameters obtained from one
> regression in another regression with a subset of the data.
That makes no sense to me: do you just want to predict the fit on a 
subset? If so use predict() or fitted().
> Are either of these possible in R?  I have been searching the help guide
for
> hours and have been unsuccessful.
Not sure what 'the help guide' is, but you need a book about doing 
statistics with R.


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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