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Calculate achieved ANOVA power at a fixed sample size

Source: R/power_effect_calc.R
power_achieved_calc.Rd

Calculation-only counterpart to power_achieved(). Numerator and denominator degrees of freedom, noncentrality, and achieved power are calculated directly without simulating data or fitting ANOVA models.

Usage

power_achieved_calc(
  between = NULL,
  within = NULL,
  term,
  target_pes,
  n,
  alpha = 0.05,
  gpower = FALSE,
  epsilon = 1
)

Arguments

between

Named integer vector of between-subject factor level counts, e.g. c(group = 2). Use NULL for no between-subject factors.

within

Named integer vector of within-subject factor level counts, e.g. c(time = 3, condition = 4). Use NULL for no within-subject factors.

term

Character scalar naming the ANOVA term to test, e.g. "group:time". Interaction terms are order-insensitive; "time:group" resolves to "group:time" when that is the design's factor order.

target_pes

Target partial eta squared for term.

n

Number of subjects per between-subject cell. For a purely within-subject design, this is the total sample size.

alpha

Significance threshold.

gpower

Logical; if TRUE, use the GPower-style noncentrality convention lambda = total_n * f^2. The default FALSE uses lambda = den_df * f^2. GPower's estimates can differ from target_pes, especially for small samples or terms with more degrees of freedom; a warning is issued when gpower = TRUE. The default gpower = FALSE is recommended.

epsilon

Population nonsphericity correction for the within-subject component of term. Must lie between the theoretical lower bound 1 / within_term_df and 1. The default 1 assumes sphericity. Values below 1 multiply the numerator degrees of freedom, denominator degrees of freedom, and noncentrality parameter. Nonsphericity corrections do not apply to purely between-subject terms.

Value

An anovapowersim_achieved_power object. $achieved_power and $calculated_power contain the calculated-power estimate. In $results, simulation-specific result columns are NA because no simulations are run.

Lifecycle

[Experimental]

power_achieved_calc() is experimental and is available only in the development version of anovapowersim. Its API and reporting format may change.

Examples

power_achieved_calc(
  between = c(group = 2),
  within = c(time = 3),
  term = "group:time",
  target_pes = 0.08,
  n = 30,
  gpower = TRUE,
  epsilon = 0.80
)
#> Warning: `gpower = TRUE` calibrates means to G*Power's noncentrality convention, so the partial eta squared actually achieved can differ from `target_pes` -- this is more pronounced for small samples and terms with more degrees of freedom. The default `gpower = FALSE` is recommended if you want `target_pes` to match your reported or expected partial eta squared exactly.
#> <anovapowersim_achieved_power>
#>   term:             'group:time'
#>   fixed n per cell: 30
#>   fixed total N:    60
#>   target pes:       0.0800
#>   alpha:            0.05
#>   calculation:      calculated power only
#>   achieved power:   0.453 (calculated)
#>   calculated power: 0.453
#>   G*Power convention: TRUE
#>   epsilon:          0.8
#> 
#>  n_per_cell total_n n_sims valid_sims failed_sims epsilon num_df den_df   ncp
#>          30      60     NA         NA          NA     0.8    1.6   92.8 4.174
#>  power_calc power_sim
#>       0.453      <NA>