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st: xsampsi produces inconsistent results
From
Michael McCulloch <[email protected]>
To
Statalist Statalist <[email protected]>
Subject
st: xsampsi produces inconsistent results
Date
Sat, 5 Jun 2010 18:37:08 -0700
Hello,
I'm using -xsampsi- to estimate sample sizes for a crossover experiment.
I compared two examples, each with alpha=0.25, and beta=0.20.
Experiment 1 (where mean difference =30, and its standard deviation =
45):
xsampsi, alpha(0.025) beta(0.20) delta(30) stddev(45)
Experiment 2 (where mean difference =2.3, and its standard deviation
= 0.63):
xsampsi, alpha(0.025) beta(0.20) delta(2.3) stddev(.63)
The first example produces a result, but the second leads to error
message:
"Need to install package 'nct' to compute non-central t distribution"
However, I have installed -nct-.
Any feedback would be appreciated!
Best wishes,
Michael McCulloch, LAc MPH PhD
Pine Street Foundation
124 Pine Street
San Anselmo, CA 94960-2674
tel: 415-407-1357
fax: 206-338-2391
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