[R] confidence interval in "predict.lm"

[Matej Cepl]

Thomas Lumley wrote:
> You asked R for a confidence interval for the predicted mean at x.  If you
> want a prediction interval at x you need  interval="prediction" not
> interval="confidence".

Slightly OT question to this thread:

How can I get critical values for given distribution density?
E.g. function f which would give me 2.228 for ft(p=0.05,df=10)
(i.e., t for student distribution with given level probability).

Sorry for newbie question.

Matej


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