[R] se's and CI's for fitted lines in multivariate regression analysis

Sigrid s.stenerud at gmail.com
Wed Oct 10 15:49:14 CEST 2012

I’m entirely stumped on this particular issue and really hoping someone has
some advice for me.
I am running a covariant model in lm I would like to give the standard
errors or the confidence intervals for the fitted lines. I’ve been using the
dataset OrangeSprays where I want lines for each level of treatment over the
covariant ‘colpos’. I’ve been able to calculate intercepts and slopes for
each lines by adding up the parameters, but this does not make sense when
the comes to the se’s.  I’ve run the summary (model) function, but only get
the differences in standard error between lines. Also by running
confint(model), I have the same problem.

How can I get standard error per or the CI-interval for each fitted line?
I’ve attached the coding underneath.

Thank you,

> data(OrchardSprays)
> model<-lm(decrease~rowpos+colpos+treatment+treatment:colpos)
> summary(model)

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