R/interpret_cohens_d.R

In easystats/effectsize: Indices of Effect Size

#' Interpret Standardized Differences
#'
#' Interpretation of standardized differences using different sets of rules of
#' thumb.
#'
#'
#' @param d,g,delta Value or vector of effect size values.
#' @param rules Can be `"cohen1988"` (default), `"gignac2016"`,
#'   `"sawilowsky2009"`, `"lovakov2021"` or a custom set of [rules()].
#' @param ... Not directly used.
#'
#' @section Rules:
#'
#' Rules apply to equally to positive and negative *d* (i.e., they are given as
#' absolute values).
#'
#' - Cohen (1988) (`"cohen1988"`; default)
#'   - **d < 0.2** - Very small
#'   - **0.2 <= d < 0.5** - Small
#'   - **0.5 <= d < 0.8** - Medium
#'   - **d >= 0.8** - Large
#' - Sawilowsky (2009) (`"sawilowsky2009"`)
#'   - **d < 0.1** - Tiny
#'   - **0.1 <= d < 0.2** - Very small
#'   - **0.2 <= d < 0.5** - Small
#'   - **0.5 <= d < 0.8** - Medium
#'   - **0.8 <= d < 1.2** - Large
#'   - **1.2 <= d < 2** - Very large
#'   - **d >= 2** - Huge
#' - Lovakov & Agadullina (2021) (`"lovakov2021"`)
#'   - **d < 0.15** - Very small
#'   - **0.15 <= d < 0.36** - Small
#'   - **0.36 <= d < 0.65** - Medium
#'   - **d >= 0.65** - Large
#' - Gignac & Szodorai (2016) (`"gignac2016"`, based on the [d_to_r()] conversion, see [interpret_r()])
#'   - **d < 0.2** - Very small
#'   - **0.2 <= d < 0.41** - Small
#'   - **0.41 <= d < 0.63** - Moderate
#'   - **d >= 0.63** - Large
#'
#' @examples
#' interpret_cohens_d(.02)
#' interpret_cohens_d(c(.5, .02))
#' interpret_cohens_d(.3, rules = "lovakov2021")
#' @references
#' - Lovakov, A., & Agadullina, E. R. (2021). Empirically Derived Guidelines for
#' Effect Size Interpretation in Social Psychology. European Journal of Social
#' Psychology.
#'
#' - Gignac, G. E., & Szodorai, E. T. (2016). Effect size guidelines for
#' individual differences researchers. Personality and individual differences,
#' 102, 74-78.
#'
#' - Cohen, J. (1988). Statistical power analysis for the behavioral sciences
#' (2nd Ed.). New York: Routledge.
#'
#' - Sawilowsky, S. S. (2009). New effect size rules of thumb.
#'
#' @keywords interpreters
#' @export
interpret_cohens_d <- function(d, rules = "cohen1988", ...) {
  if (is.character(rules) && rules == "gignac2016") {
    return(interpret_r(d_to_r(d), rules))
  }

  rules <- .match.rules(
    rules,
    list(
      cohen1988 = rules(c(0.2, 0.5, 0.8), c("very small", "small", "medium", "large"),
        name = "cohen1988", right = FALSE
      ),
      sawilowsky2009 = rules(c(0.1, 0.2, 0.5, 0.8, 1.2, 2),
        c("tiny", "very small", "small", "medium", "large", "very large", "huge"),
        name = "sawilowsky2009", right = FALSE
      ),
      lovakov2021 = rules(c(0.15, 0.36, 0.65),
        c("very small", "small", "medium", "large"),
        name = "lovakov2021", right = FALSE
      ),
      gignac2016 = NA # added for the correct error msg
    )
  )

  interpret(abs(d), rules)
}

#' @rdname interpret_cohens_d
#' @export
interpret_hedges_g <- function(g, rules = "cohen1988") {
  interpret_cohens_d(g, rules)
}

#' @rdname interpret_cohens_d
#' @export
interpret_glass_delta <- function(delta, rules = "cohen1988") {
  interpret_cohens_d(delta, rules)
}