[R] How to specify a fixed intercept for linear model

[Michael Bedward]

The offset arg is your friend...

x <- 1:10
y <- 42 + 2*x + rnorm(length(x), 0, 0.5)

# we suspect the intercept might be 42 !
lm( y ~ 0 + x, offset=rep(42, length(x)))

Michael


On 4 December 2010 13:42, cborley87
<christopher.borley at students.plymouth.ac.uk> wrote:
>
> Hi,
>
> Im fitting some simple linear models to data from the olympic running events
> with lm(Logtime~Logdistance), the models contain an intercept and one slope
> parameter.
>
> I have fitted a separate model for each years data and as the intercept
> changes very little between years i am trying to simplify the models so that
> they all have the same intercept (calculated from the mean of the previous
> intercepts).
>
> I have seen a few posts relating to zero intercepts but cannot figure out
> how to set to a specific value to the parameter.
>
> Any help would be greatly appreciated.
>
> Thanks.
>
> Chris.
> --
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