[R] lm help: using lm when one point is known (not y intercept)

[John Fox]

Dear Seth,

You don't say which variable is the explanatory variable and which is the
response, but assuming that prob is to be regressed on effect, you can fit
lm(prob - 50 ~ I(effect + 37.25) - 1). That is you can shift the point
through which the regression is to go to the origin and then force the
regression through the origin.

I hope this helps,
 John

--------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario
Canada L8S 4M4
905-525-9140x23604
http://socserv.mcmaster.ca/jfox 
-------------------------------- 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Seth Imhoff
> Sent: Saturday, November 27, 2004 11:09 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] lm help: using lm when one point is known (not y 
> intercept)
> 
> Hello-
> 
> My question is a short one.  How can I specify a single point 
> which through the fitted linear model has to go through?  To 
> illustrate my problem, the fit to following data must go 
> through the point (-37.25(effect), 50(prob)).  Note: you can 
> ignore the label column.
> 
>     Effect      Prob Label
> 
> 1 -1143.75  7.142857     L
> 
> 2  -572.75 21.428571     D
> 
> 3  -223.75 35.714286    GL
> 
> 4   123.25 50.000000    DG
> 
> 5   359.75 64.285714     G
> 
> 6   374.75 78.571429   DGL
> 
> 7   821.75 92.857143    DL
> 
> 
> Thanks in advance!
> 
> Seth Imhoff