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⇤ ← Revision 1 as of 2008-01-21 16:53:52
Size: 526
Comment:
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Size: 527
Comment:
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| Deletions are marked like this. | Additions are marked like this. |
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| (pow - (1 - pt(abs(qt(alph/2,(2*n)-2)),mdiff/sqrt((2*sd*sd)/n*(1-rho))) )^2 | (pow - (1 - pt(abs(qt(alph/2,(2*n)-2)),mdiff/sqrt((2*sd*sd)/n*(1-rho)))) )^2 |
Sample sizes for paired t in R
mdiff is the difference between the two variables with correlation, rho, type I error, alpha, and (common) sd.
[COPY AND PASTE INTO R AND ADJUST INPUTS AS DESIRED]
pow <- 0.8 alpha <- 0.05 mdiff <- 2 sd <- 4 rho <- 0.5
[THEN COPY AND PASTE THE BELOW INTO R] [OUTPUTS NUMBER OF PAIRS]
fn <- function(n) {
(pow - (1 - pt(abs(qt(alph/2,(2*n)-2)),mdiff/sqrt((2*sd*sd)/n*(1-rho)))) )^2
}
nout<- nlm(fn,2)
nout<- trunc(nout$estimate+1)
print(nout)