R help - Oct 2008 - syntax to restrict coefficient in lm()

Hi,

I would like to estimate an error correction model with lm() but I don't
find the correct syntax for that.
The model (leaving out the time indices) looks like:

dY = a0 - a1 * (Y - b1*X) + b0*dX + e

the problem is the term - a1 * (Y - b1*X). How can I restrict a1 to be the same
for both Y and -b1*X ?

Thanks for considering my question!

All the best,
  Werner

On 04/10/2008 3:29 PM, Werner Wernersen wrote:
> Hi,
> 
> I would like to estimate an error correction model with lm() but I
don't find the correct syntax for that.
> The model (leaving out the time indices) looks like:
> 
> dY = a0 - a1 * (Y - b1*X) + b0*dX + e
> 
> the problem is the term - a1 * (Y - b1*X). How can I restrict a1 to be the
same for both Y and -b1*X ?
lm() fits linear models, and that's not parametrized as a linear model. 
  It is equivalent to this linear model:

dY = a0 + a1 * Y + a2 * X + b0 * dX + e

where I have changed the sign of a1, and replaced a1*b1 with a2.  You 
can specify that model in lm() as

dY ~ Y + X + dX

Duncan Murdoch
> 
> Thanks for considering my question!
> 
> All the best,
>   Werner
> 
> 
> 
> 
> 
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