Regression slope confidence interval

?confint

Thank you to all of you.

As far as I see this is not mentioned on the lm help page (though I
presumably don't have the recent version), which I would
suggest...

and I would suggest that you study a good book on the subject.

(confint and its lm method come from MASS.  It is not specific to lm. 
There are lots of applicable generics not mentioned on the help pages of 
specific model-fitting functions.)

help.search("confidence interval") does get you there, for example.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595