[R] Bad points in regression

[(Ted Harding)]

On 16-Mar-07 11:56:56, Alberto Monteiro wrote:
> I have a question, maybe it's better to explain by example:
> 
> alpha <- 0.3
> beta <- 0.4
> sigma <- 0.5
> err <- rnorm(100)
> err[15] <- 5; err[25] <- -4; err[50] <- 10
> x <- 1:100
> y <- alpha + beta * x + sigma * err
> ll <- lm(y ~ x)
> plot(ll)
> 
> Now, the graphs clearly show that 15, 25 and 50 are the indexes
> of the bad points. How can I retrieve this information from ll?
> 
> Alberto Monteiro

ll is the output of a linear model fiited by lm(), and so has
several components (see ?lm in the section "Value"), one of
which is "residuals" (which can be abbreviated to "res").

So, in the case of your example,

  which(abs(ll$res)>2)
  15 25 50 

extracts the information you want (and the ">2" was inspired by
looking at the "residuals" plot from your "plot(ll)").

Best wishes,
Ted.

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Date: 16-Mar-07                                       Time: 12:19:02
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