power.anova.test {ctest} R Documentation

## Power calculations for balanced one-way analysis of variance tests

### Description

Compute power of test or determine parameters to obtain target power.

### Usage

```power.anova.test(groups = NULL, n = NULL, between.var = NULL,
within.var = NULL, sig.level = 0.05, power = NULL)
```

### Arguments

 `groups` Number of groups `n` Number of observations (per group) `between.var` Between group variance `within.var` Within group variance `sig.level` Significance level (Type I error probability) `power` Power of test (1 minus Type II error probability)

### Details

Exactly one of the parameters `groups`, `n`, `between.var`, `power`, `within.var`, and `sig.level` must be passed as NULL, and that parameter is determined from the others. Notice that `sig.level` has non-NULL default so NULL must be explicitly passed if you want it computed.

### 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)

Claus Ekstrřm

`anova`, `lm`, `uniroot`

### Examples

```power.anova.test(groups=4, n=5, between.var=1, within.var=3)
# Power = 0.3535594

power.anova.test(groups=4, between.var=1, within.var=3,
power=.80)
# n = 11.92613

## Assume we have prior knowledge of the group means:
groupmeans <- c(120, 130, 140, 150)
power.anova.test(groups = length(groupmeans),
between.var=var(groupmeans),
within.var=500, power=.90) # n = 15.18834

```

[Package Contents]