Superpower (version 0.2.4)

power_oneway_ancova: Power Calculations for a one-way ANCOVA

Description

Compute power of ANCOVA omnibus test (power_oneway_ancova) or contrast (power_oneway_ancova) for one-way (single factor), between subjects designs.

Usage

power_oneway_ancova(
  n = NULL,
  mu = NULL,
  n_cov = 1,
  r2 = NULL,
  sd = 1,
  alpha_level = Superpower_options("alpha_level"),
  beta_level = NULL,
  round_up = TRUE,
  type = "exact"
)

Value

dfs = degrees of freedom, N = Total sample size, n = Sample size per group/condition, n_cov = Number of covariates, mu = Mean for each condition, sd = Standard deviation, r2 = Coefficient of determination of combined covariates. alpha_level = Type 1 error probability, beta_level = Type 2 error probability, power = Power of test (1-beta_level\*100

type = Method (Shieh or Keppel) for estimating power

Arguments

n

Sample size in each condition.

mu

Vector specifying mean for each condition.

n_cov

Number of covariates.

r2

Coefficient of determination (r^2) of the combined covariates.

sd

Standard deviation for all conditions (residual SD without covariate adjustment).

alpha_level

Alpha level used to determine statistical significance.

beta_level

Type II error probability (power/100-1)

round_up

Logical indicator for whether to round up the sample size(s) to a whole number. Default is TRUE.

type

Sets the method for estimating power. "exact" will use the Shieh (2020) approach while "approx" will use the Keppel (1991) approach.

References

Keppel, G. (1991). Design and Analysis A Researcher's Handbook. 3rd Edition. Prentice Hall. Englewood Cliffs, New Jersey. See pages 323 - 324. Shieh, G. (2017). Power and sample size calculations for contrast analysis in ANCOVA. Multivariate behavioral research, 52(1), 1-11. Shieh, G. (2020). Power analysis and sample size planning in ANCOVA designs. Psychometrika, 85(1), 101-120.

Examples

# Example from Table 1 Shieh 2020
power_oneway_ancova(mu = c(400, 450, 500), n = c(21,21,21),
r2 = .1^2, sd = 100)