pwr.t.test: Power calculations for t-tests of means (one sample, two...
In pwr: Basic Functions for Power Analysis

Description Usage Arguments Details Value Note Author(s) References See Also Examples

Compute power of tests or determine parameters to obtain target power (similar to power.t.test).

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pwr.t.test(n = NULL, d = NULL, sig.level = 0.05, power = NULL, 
    type = c("two.sample", "one.sample", "paired"),
    alternative = c("two.sided", "less", "greater"))

`n`	Number of observations (per sample)
`d`	Effect size (Cohen's d) - difference between the means divided by the pooled standard deviation
`sig.level`	Significance level (Type I error probability)
`power`	Power of test (1 minus Type II error probability)
`type`	Type of t test : one- two- or paired-samples
`alternative`	a character string specifying the alternative hypothesis, must be one of "two.sided" (default), "greater" or "less"

Exactly one of the parameters 'd','n','power' and 'sig.level' must be passed as NULL, and that parameter is determined from the others. Notice that the last one has non-NULL default so NULL must be explicitly passed if you want to compute it.

Object of class '"power.htest"', a list of the arguments (including the computed one) augmented with 'method' and 'note' elements.

'uniroot' is used to solve power equation for unknowns, so you may see errors from it, notably about inability to bracket the root when invalid arguments are given.

Stephane Champely <champely@univ-lyon1.fr> but this is a mere copy of Peter Dalgaard work (power.t.test)

Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed.). Hillsdale,NJ: Lawrence Erlbaum.

power.prop.test

## One sample (power)
## Exercise 2.5 p. 47 from Cohen (1988)
pwr.t.test(d=0.2,n=60,sig.level=0.10,type="one.sample",alternative="two.sided")

## Paired samples (power)
## Exercise p. 50 from Cohen (1988)
d<-8/(16*sqrt(2*(1-0.6)))
pwr.t.test(d=d,n=40,sig.level=0.05,type="paired",alternative="two.sided")

## Two independent samples (power)
## Exercise 2.1 p. 40 from Cohen (1988)
d<-2/2.8
pwr.t.test(d=d,n=30,sig.level=0.05,type="two.sample",alternative="two.sided")

## Two independent samples (sample size)
## Exercise 2.10 p. 59
pwr.t.test(d=0.3,power=0.75,sig.level=0.05,type="two.sample",alternative="greater")