On 01.10.2014 14:29, Stephen Kennedy 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?
Vector of ’n’ s
power.t.test(n=c(28,29,30), delta=2, sd=3, sig.level=0.05, type="two.sample",
alternative="one.sided")
Two-sample t test power calculation
n = 28, 29, 30
delta = 2
sd = 3
sig.level = 0.05
power = 0.7933594, 0.8058963, 0.8177506
alternative = one.sided
NOTE: n is number in *each* group
Vector of ‘power’ s
power.t.test(power=c(0.7,0.8,0.9), delta=2, sd=3, sig.level=0.05, type="two.sample",
alternative="one.sided")
Error in uniroot(function(n) eval(p.body) - power, c(2, 1e+07)) :
f() values at end points not of opposite sign
In addition: Warning messages:
1: In if (is.na(f.lower)) stop("f.lower = f(lower) is NA") :
the condition has length > 1 and only the first element will be used
2: In if (is.na(f.upper)) stop("f.upper = f(upper) is NA") :
the condition has length > 1 and only the first element will be used
power.t.test oes not work on vectors in general.
Here, you want:
lapply(c(0.7, 0.8, 0.9),
function(power)
power.t.test(power=power, delta=2, sd=3, sig.level=0.05,
type="two.sample", alternative="one.sided")
)
Best,
Uwe Ligges
Thanks,
Steve
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