effsize: Effect size calculation

In extraSuperpower: Power Calculation for Two-Way Factorial Designs

Effect size calculation

Description

Calculate effect sizes for two-way factorial designs from matrices of expected mean and standard deviation values at each combination of factor levels. The output given is Cohen's f. Calculations are done as exemplified in the G*Power 3.1 manual.

Usage

effsize(matrices_obj)

Arguments

matrices_obj

List of 2 matrices, named mean.mat and sd.mat. This is the minimal output of the calculate_mean_matrix function. The full output from calculate_mean_matrix is also valid.

Value

Vector of length 3. The first two elements are the effect sizes for the main effects factor A and factor B, respectively. The third element is the interaction effect size.

Examples

# no interaction effect expected
refmean <- 1
treatgroups <- 4
timepoints <- 5
treateff <- 1.5
timeeff <- 0.85

factors_levels_names <- list(treatment=letters[1:treatgroups], time=1:timepoints)

effects_treat_time <- calculate_mean_matrix(refmean = refmean,
                                            nlfA = treatgroups, nlfB = timepoints,
                                            fAeffect = treateff, fBeffect = timeeff,
                                            label_list = factors_levels_names)
effsize(effects_treat_time)

# we add cell specific interaction effect keeping design and main effect coefficients
cellswithinteraction <- matrix(c(rep(2,3), 3:5), 3,2)
#second level of factor A interacts with 3rd, 4th and 5th level of factor B

effects_treat_time_interact <- calculate_mean_matrix(refmean = refmean,
                                                     nlfA = treatgroups, nlfB = timepoints,
                                                     fAeffect = treateff, fBeffect = timeeff,
                                                     label_list = factors_levels_names,
                                                     groupswinteraction = cellswithinteraction,
                                                     interact=1.3)
effsize(effects_treat_time_interact)

extraSuperpower documentation built on Aug. 8, 2025, 6:44 p.m.