[R] How to fix slope and estimate intercept

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Jun Shen
> Sent: Thursday, July 22, 2010 10:30 AM
> To: R-help
> Subject: [R] How to fix slope and estimate intercept
> 
> Dear all,
> 
> Is there anyway I can fix slope in some value and only estimate
> intercept for a linear regression? I understand lm(y~1, data) will NOT
> have a slope at all. This is not what I want. Thanks.

You can use an offset() term in your formula.  E.g.,
  > x <- log(1:10)
  > y <- 2.7*x + 3.4
  > lm(y ~ 1 + offset(2.7*x))
  
  Call:
  lm(formula = y ~ 1 + offset(2.7 * x))

  Coefficients:
  (Intercept)  
          3.4  

  > lm(y ~ 1 + offset(2.6*x))

  Call:
  lm(formula = y ~ 1 + offset(2.6 * x))

  Coefficients:
     (Intercept)  
  3.551044125731  

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  

> 
> Jun
> 
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