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 Ekstrøm

### See Also

`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