powertools (version 1.0.0)

multisite.cont: Power for test of average treatment effect in a multisite trial

Description

Performs power and sample size calculations for a multisite trial with a continuous (normal) outcome variable. Can solve for power, J, m or alpha.

Usage

multisite.cont(
  m = NULL,
  m.sd = 0,
  alloc.ratio = 1,
  J = NULL,
  delta = NULL,
  sd = 1,
  icc0 = NULL,
  icc1 = NULL,
  Rsq = 0,
  alpha = 0.05,
  power = NULL,
  sides = 2,
  v = FALSE
)

Value

A list of the arguments (including the computed one).

Arguments

m

The mean cluster/site size (number of participants per site).

m.sd

The standard deviation of cluster/site sizes (provide if unequal number of participants per site); defaults to 0.

alloc.ratio

The allocation ratio of condition 2/condition 1 within site; defaults to 1.

J

The total number of sites.

delta

The difference between the condition 1 and condition 2 means under the alternative minus the difference under the null hypothesis.

sd

The total standard deviation of the outcome variable; defaults to 1.

icc0

The proportion of total variance of the outcome attributable to variation in site-level means.

icc1

The proportion of total variance of the outcome attributable to variation in the treatment effect across sites.

Rsq

The estimated R^2 for regressing the outcome on the covariates; defaults to 0.

alpha

The significance level (type 1 error rate); defaults to 0.05.

power

The specified level of power.

sides

Either 1 or 2 (default) to specify a one- or two- sided hypothesis test.

v

Either TRUE for verbose output or FALSE (default) to output computed argument only.

Details

In a multisite trial design, participants are randomized to conditions within site.

Examples

multisite.cont(m = 20, J = 10, delta = 3, sd = sqrt(40), icc0 = 0.1, icc1 = 0)
multisite.cont(m = 20, J = 10, delta = 3, sd = sqrt(48), icc0 = 0.095, icc1 = 0.048)
multisite.cont(m = 20, alloc.ratio = 1.5, J = 10, delta = 0.43, icc0 = 0.095, icc1 = 0.048)
multisite.cont(m = 10, J = NULL, delta = 0.5, sd = 1, icc0 = 0, icc1 = 0.05, power = 0.8)
multisite.cont(m = 20, m.sd = 5, J = 10, delta = 3, sd = sqrt(48), icc0 = 0.095, icc1 = 0.048)
multisite.cont(m = 20, J = 10, delta = 3, sd = sqrt(48), icc0 = 0.095,
icc1 = 0.048, Rsq = 0.5^2)