R: Power calculations for two samples (different sizes) t-tests...

pwr.t2n.test {pwr} | R Documentation

## Power calculations for two samples (different sizes) t-tests of means

### Description

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

### Usage

    pwr.t2n.test(n1 = NULL, n2= NULL, d = NULL, sig.level = 0.05, power = NULL,
     alternative = c("two.sided",
            "less","greater"))

### Arguments

`n1` | Number of observations in the first sample
`n2` | Number of observations in the second sample
`d` | Effect size
`sig.level` | Significance level (Type I error probability)
`power` | Power of test (1 minus Type II error probability)
`alternative` | a character string specifying the alternative hypothesis, must be one of "two.sided" (default), "greater" or "less"

### Details

Exactly one of the parameters 'd','n1','n2','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.

### Value

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

### Note

'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.

### Author(s)

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

### References

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

### Examples

    ## Exercise 2.3 p. 437 from Cohen (1988)
    pwr.t2n.test(d=0.6,n1=90,n2=60,alternative="greater")

[Package pwr version 1.2-2 Index]