Dear Professor Dalgard,
I wondered if I might ask a general question on ‘power’. Please feel free to
ignore.
For ‘non-inferiority’ clinical trials:
H0: m1 - m2 ≤ -M
Ha: m1 - m2 > -M
But when calculations are done (normal, t, or non-central t … still learning
what this is),
Ha: m1 - m2 = 0
is assumed (for power, n, …) .
Why not average (integrate numerically) the results from -M to infinity and
keep the original alternative hypothesis?
In fact, calculation of the Type I error is made assuming m1 - m2 = -M, which
doesn’t seem strictly accurate either.
Best,
Steve
Stephen J. Kennedy, Ph.D.
Director, Research & Development
Prollenium Medical Technologies, Inc.
138 Industrial Parkway North
Aurora, ON
L4G 4C3 Canada
+1 (905) 508-1469 X223
step...@prollenium.com
On Oct 1, 2014, at 6:46 PM, peter dalgaard <pda...@gmail.com> wrote:
On 01 Oct 2014, at 14:29 , Stephen Kennedy <step...@prollenium.com> wrote:
> Simple question. A vector of ‘number of observations’ can be input to
> power.t.test, and a vector of ‘power’ s is output. But, inputting a vector
> of powers generates an error. Am I missing something?
Power.t.test was written for scalar arguments. If it happens to work with
vector arguments, it is entirely coincidental. The essence of what you observe
is that power is calculated by pt() which vectorizes, but n is calculated by
numerical solution using uniroot() which does not vectorize.
If you need a vectorized version, check out Vectorize().
--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd....@cbs.dk Priv: pda...@gmail.com
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