# pwr.t2n.test

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

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

- Keywords
- htest

##### 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.

##### References

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

##### Examples

```
# NOT RUN {
## Exercise 2.3 p. 437 from Cohen (1988)
pwr.t2n.test(d=0.6,n1=90,n2=60,alternative="greater")
# }
```

*Documentation reproduced from package pwr, version 1.2-2, License: GPL (>= 3)*