[R] use of predict() with confidence/prediction bands

Alan Arnholt arnholt at cs.cs.appstate.edu
Thu Dec 29 19:41:10 CET 2005

To my understanding, a confidence interval typically covers a single
valued parameter.  In contrast, a confidence band covers an entire line
with a band.  In regression, it is quite common to construct confidence
and prediction bands.  I have found that many people are connecting
individual confidence/prediction interval values produced with
predict(object,sd.fit=T,type="conf/pred") and calling the result a
confidence/prediction band.  Since there is no specific probability
statement that can be attached to these connected confidence/prediction
intervals, this does not seem reasonable to me.  This is done, for
example, in ISWR pg. 105, UsingR for Introductory Statistics pg 296, and
Linear Models with R pg. 39 (Although in this instance the intervals are
called 95% "pointwise" confidence bands versus simply 95% confidence
bands.)  To make a confidence/prediction band, one should  construct
simultaneous confidence/prediction intervals with say a Scheffe approach
as mentioned in the S-PLUS Guide to statistics pg 274.  If these connected
intervals were called pointwise confidence/prediction intervals with the
understanding that have no particular probability interpretation, then
they are useful in understanding where the line should fall.  However,
they are not confidence/prediction bands as such, and I think it is
misleading to name them so.  Should the intervals the authors in the
three mentioned references construct not be called something similar
to connected 95% pointwise confidence/prediction intervals versus 95%
confidence/prediction bands?  Or, have I missed the boat?  Fire away...

Alan T. Arnholt
Associate Professor
Dept. of Mathematical Sciences
Appalachian State University

More information about the R-help mailing list