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st: Power calculation for regression

From   "Wallace, John" <>
To   "''" <>
Subject   st: Power calculation for regression
Date   Mon, 23 Feb 2004 10:36:11 -0800

Dear Statalisters

I'm putting together a prospective protocol for a long term stability study
(26 months) that will ultimately yield a series of 17 data points over time.
Each data point will be an average of 5 replicates from a test.  I
anticipate plotting a regression of average intensity (the test result)over
time, to yield a linear equation.  Is there a common test for inferring an
effect due to time, such as rejecting a null hypothesis of slope=0?  Can I
calculate power? Are five replicates at each point sufficient?

Thanks for any guidance - even if its RTFM (though a pointer to a specific
section would be appreciated - the help file for -regress- is dizzyingly

John Wallace | Research Associate | Test Method Development
AFFYMETRIX, INC. | 3380 Central Expressway | Santa Clara, CA 95051 | Tel:
408-731-5574 | Fax:  408-481-0435
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