[R] power.t.test

Marc Schwartz mschwartz at medanalytics.com
Mon Mar 31 22:58:51 CEST 2003

>-----Original Message-----
>From: r-help-bounces at stat.math.ethz.ch 
>[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Hank Stevens
>Sent: Monday, March 31, 2003 2:43 PM
>To: r-help at stat.math.ethz.ch
>Subject: [R] power.t.test
>power.t.test() requires a standard deviation as input, but for 
>a two sample 
>test, I do not understand what is required. Is it the standard 
>deviation of 
>the means (standard error), or of the combined sample?
>Hank Stevens

The 'sd' argument is the standard deviation of the mean for *each*
sample, keeping in mind that the underlying assumption is that both
samples have equal variances.  Thus you need only specify one value.


Marc Schwartz

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