R help - Jul 2011 - help with regression

Hi,

I am trying to do a linear regression but I want one of my variables to not
generate a coefficient.  E.g. what I want to do is fit for y=a+b+c but
forcing the coefficient of b to be 1.  Is this possible?  

I have been fitting y-b=a+c but I have found that when I recalculate y it is
not close to the value.  I have assumed that by fitting y-b then the y part
has become insignificant.  In case it makes a difference I have been using
lm rather than glm.

Thanks in advance,

Joe

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Dear Joe,

You need to use offset()
lm(y ~ a + offset(b) + c)

Best regards,

Thierry

----------------------------------------------------------------------------
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Gaverstraat 4
9500 Geraardsbergen
Belgium

Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium

tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more than
asking him to perform a post-mortem examination: he may be able to say what the
experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not ensure
that a reasonable answer can be extracted from a given body of data.
~ John Tukey

> -----Oorspronkelijk bericht-----
> Van: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org]
> Namens JoeP
> Verzonden: dinsdag 26 juli 2011 11:26
> Aan: r-help at r-project.org
> Onderwerp: [R] help with regression
> 
> Hi,
> 
> I am trying to do a linear regression but I want one of my variables to not
> generate a coefficient.  E.g. what I want to do is fit for y=a+b+c but
forcing the
> coefficient of b to be 1.  Is this possible?
> 
> I have been fitting y-b=a+c but I have found that when I recalculate y it
is not
> close to the value.  I have assumed that by fitting y-b then the y part has
become
> insignificant.  In case it makes a difference I have been using lm rather
than glm.
> 
> Thanks in advance,
> 
> Joe
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/help-with-
> regression-tp3695245p3695245.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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