anovapowersim

anovapowersim is designed to make determining a priori power for ANOVAs as easy as possible. You can add as many within/between factors with as many levels as you would like. There’s no need to estimate condition means, SDs, or repeated-measures correlations; just enter the target partial eta squared.

The package simulates data and estimates power based on the specified design. It also provides direct power calculations for comparison.

Getting a priori power for a 2 × 2 × 3 mixed interaction effect is as simple as running the following:

library(anovapowersim)

power_n(
  between = c(group = 2), # group has 2 levels
  within = c(stim = 2, cond = 3), # stim has 2 levels, cond has 3
  term = "group:stim:cond", # three-way interaction term
  target_pes = 0.08, # target effect size
  n_sims = 5000, # increase to 10000+ for more precise estimates
  power = .80,
  alpha = .05,
  parallel = TRUE, # simulations will be run in parallel for speed
  seed = 123 # for reproducibility
)

#><anovapowersim_curve>
#>  term:          'group:stim:cond'
#>  target power:  0.800
#>  alpha:         0.05
#>  effect size:   pes = 0.08
#>  n values:      7 per-cell sample sizes visited
#>  sims per cell size: 5000
#>  n needed for between-subjects cell: 30
#>  total N needed: 60
#>
#> n_per_cell total_n n_sims num_df den_df    ncp power_calc power_sim
#>         24      48   5000      2     92  8.000      0.702     0.702
#>         27      54   5000      2    104  9.043      0.760     0.758
#>         28      56   5000      2    108  9.391      0.777     0.787
#>         29      58   5000      2    112  9.739      0.793     0.796
#>         30      60   5000      2    116 10.087      0.808     0.817
#>         36      72   5000      2    140 12.174      0.881     0.886
#>         48      96   5000      2    188 16.348      0.958     0.961

Installation

anovapowersim is currently in development. You can install it from GitHub using the devtools package:

# Install devtools if you haven't already
install.packages("devtools")

# Install anovapowersim from GitHub
devtools::install_github("shaheedazaad/anovapowersim")

Citation

A preprint is in preparation.

Limitations

anovapowersim is designed to be simple and easy to use first, which means it has some limitations for now. It does not support:

• Covariates (ANCOVAs)
• Means-based simulations for unbalanced designs
• Nonsphericity corrections (though this might change)
• Specific interaction shapes (based on means)
• Simple main effects/pairwise comparisons

Other packages

I recommend checking out Superpower, which handles some of the limitations above.