power.anova.test            package:stats            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

