pwr (version 1.2-0)

pwr.t2n.test: 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"

Value

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

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.

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")