Etienne,

For this type of graph, I would use the functions in the HH package

## install.packages("HH")  ## if necessary
library(HH)

 normal.and.t.dist(std.dev=2, Use.alpha.left=FALSE, deg.free=6,
                   mu.H1=2, Use.mu.H1=TRUE,
                   obs.mean=2.5, Use.obs.mean=TRUE, xmin=-7)

Rich


On Tue, May 24, 2011 at 9:08 AM, Etienne Stockhausen <einohr2002@web.de>wrote:

> Dear R-User,
>
> I'm trying to visualize the results of the power calculation with the
> function power.t.test(). Therefore I want to plot the related
> t-distributions and shade the surfaces indicatingt the type I error, the
> type II error and the power. For sample sizes greater 30 I got results which
> are very satisfying. For small sample sizes I got stuck and did'nt find a
> mistake.
>

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