coh_d {esvis}

Compute Cohen's d

Description

This function calculates effect sizes in terms of Cohen's d, also called the uncorrected effect size. See hedg_g for the sample size corrected version. Also see Lakens (2013) for a discussion on different types of effect sizes and their interpretation. Note that missing data are removed from the calculations of the means and standard deviations.

Usage

coh_d(data, formula, ref_group = NULL, se = TRUE)

Arguments

data

The data frame used for estimation - ideally structured in a tidy format.

formula

A formula of the type out ~ group where out is the outcome variable and group is the grouping variable. Note this variable can include any arbitrary number of groups. Additional variables can be included with + to produce separate estimates by the secondary or tertiary variables of interest (e.g., out ~ group + characteristic1 + characteristic2).

ref_group

Optional. A character vector or forumla listing the reference group levels for each variable on the right hand side of the formula, supplied in the same order as the formula. Note that if using the formula version, levels that are numbers, or include hyphens, spaces, etc., should be wrapped in back ticks (e.g., ref_group = ~ Active + `Non-FRL`, or ref_group = ~`8`). When in doubt, it is safest to use the back ticks, as they will not interfere with anything if they are not needed. See examples below for more details.

se

Logical. Should the standard error of the effect size be estimated and returned in the resulting data frame? Defaults to TRUE.

Value

By default the Cohen's d for all possible pairings of the grouping factor(s) are returned.

Examples

# Calculate Cohen's d for all pairwise comparisons
coh_d(star, reading ~ condition) 

# Report only relative to regular-sized classrooms
coh_d(star,
      reading ~ condition, 
		   ref_group = "reg")

# Report by ELL and FRL groups for each season, compare to non-ELL students
# who were not eligible for free or reduced price lunch in the fall (using
# the formula interface for reference group referencing).

coh_d(benchmarks, 
      math ~ ell + frl + season,
      ref_group = ~`Non-ELL` + `Non-FRL` + Fall)

# Same thing but with character vector supplied, rather than a formula
coh_d(benchmarks, 
      math ~ ell + frl + season,
      ref_group = c("Non-ELL", "Non-FRL", "Fall"))