R/interpret_r.R

In effectsize: Indices of Effect Size

#' Interpret Correlation Coefficient
#'
#' @param r Value or vector of correlation coefficient.
#' @param rules Can be `"funder2019"` (default), `"gignac2016"`, `"cohen1988"`,
#'   `"evans1996"`, `"lovakov2021"` or a custom set of [rules()].
#' @param ... Not directly used.
#'
#' @details
#' Since Cohen's _w_ does not have a fixed upper bound, for all by the most
#' simple of cases (2-by-2 or 1-by-2 tables), interpreting Cohen's _w_ as a
#' correlation coefficient is inappropriate (Ben-Shachar, et al., 2024; Cohen,
#' 1988, p. 222). Please us [cramers_v()] of the like instead.
#'
#'
#' @note As \eqn{\phi}{\phi} can be larger than 1 - it is recommended to compute
#'   and interpret Cramer's *V* instead.
#'
#' @section Rules:
#'
#' Rules apply to positive and negative *r* alike.
#'
#' - Funder & Ozer (2019) (`"funder2019"`; default)
#'   - **r < 0.05** - Tiny
#'   - **0.05 <= r < 0.1** - Very small
#'   - **0.1 <= r < 0.2** - Small
#'   - **0.2 <= r < 0.3** - Medium
#'   - **0.3 <= r < 0.4** - Large
#'   - **r >= 0.4** - Very large
#' - Gignac & Szodorai (2016) (`"gignac2016"`)
#'   - **r < 0.1** - Very small
#'   - **0.1 <= r < 0.2** - Small
#'   - **0.2 <= r < 0.3** - Moderate
#'   - **r >= 0.3** - Large
#' - Cohen (1988) (`"cohen1988"`)
#'   - **r < 0.1** - Very small
#'   - **0.1 <= r < 0.3** - Small
#'   - **0.3 <= r < 0.5** - Moderate
#'   - **r >= 0.5** - Large
#' - Lovakov & Agadullina (2021) (`"lovakov2021"`)
#'   - **r < 0.12** - Very small
#'   - **0.12 <= r < 0.24** - Small
#'   - **0.24 <= r < 0.41** - Moderate
#'   - **r >= 0.41** - Large
#' - Evans (1996) (`"evans1996"`)
#'   - **r < 0.2** - Very weak
#'   - **0.2 <= r < 0.4** - Weak
#'   - **0.4 <= r < 0.6** - Moderate
#'   - **0.6 <= r < 0.8** - Strong
#'   - **r >= 0.8** - Very strong
#'
#' @examples
#' interpret_r(.015)
#' interpret_r(c(.5, -.02))
#' interpret_r(.3, rules = "lovakov2021")
#' @seealso Page 88 of APA's 6th Edition.
#'
#' @references
#' - Lovakov, A., & Agadullina, E. R. (2021). Empirically Derived Guidelines for
#' Effect Size Interpretation in Social Psychology. European Journal of Social
#' Psychology.
#'
#' - Funder, D. C., & Ozer, D. J. (2019). Evaluating effect size in
#' psychological research: sense and nonsense. Advances in Methods and Practices
#' in Psychological Science.
#'
#' - 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.
#'
#' - Evans, J. D. (1996). Straightforward statistics for the behavioral
#' sciences. Thomson Brooks/Cole Publishing Co.
#'
#' - Ben-Shachar, M.S., Patil, I., Thériault, R., Wiernik, B.M., Lüdecke, D.
#' (2023). Phi, Fei, Fo, Fum: Effect Sizes for Categorical Data That Use the
#' Chi‑Squared Statistic. Mathematics, 11, 1982. \doi{10.3390/math11091982}
#'
#' @keywords interpreters
#' @export
interpret_r <- function(r, rules = "funder2019", ...) {
  rules <- .match.rules(
    rules,
    list(
      funder2019 = rules(c(0.05, 0.1, 0.2, 0.3, 0.4),
        c("tiny", "very small", "small", "medium", "large", "very large"),
        name = "funder2019", right = FALSE
      ),
      gignac2016 = rules(c(0.1, 0.2, 0.3),
        c("very small", "small", "moderate", "large"),
        name = "gignac2016", right = FALSE
      ),
      cohen1988 = rules(c(0.1, 0.3, 0.5),
        c("very small", "small", "moderate", "large"),
        name = "cohen1988", right = FALSE
      ),
      evans1996 = rules(c(0.2, 0.4, 0.6, 0.8),
        c("very weak", "weak", "moderate", "strong", "very strong"),
        name = "evans1996", right = FALSE
      ),
      lovakov2021 = rules(c(0.12, 0.24, 0.41),
        c("very small", "small", "medium", "large"),
        name = "lovakov2021", right = FALSE
      )
    )
  )

  interpret(r, rules, transform = abs)
}

#' @export
#' @rdname interpret_r
interpret_phi <- interpret_r

#' @export
#' @rdname interpret_r
interpret_cramers_v <- interpret_r

#' @export
#' @rdname interpret_r
interpret_rank_biserial <- interpret_r

#' @export
#' @rdname interpret_r
interpret_fei <- interpret_r