R/interpret_oddsratio.R

In effectsize: Indices of Effect Size

#' Interpret Odds Ratio
#'
#' @param OR Value or vector of (log) odds ratio values.
#' @param rules Can be "`chen2010"` (default), `"cohen1988"` (through
#'   transformation to standardized difference, see [oddsratio_to_d()]) or custom set
#'   of [rules()].
#' @param log Are the provided values log odds ratio.
#' @inheritParams interpret
#'
#' @section Rules:
#'
#' Rules apply to OR as ratios, so OR of 10 is as extreme as a OR of 0.1 (1/10).
#'
#' - Chen et al. (2010) (`"chen2010"`; default)
#'   - **OR < 1.68** - Very small
#'   - **1.68 <= OR < 3.47** - Small
#'   - **3.47 <= OR < 6.71** - Medium
#'   - **OR >= 6.71 ** - Large
#' - Cohen (1988) (`"cohen1988"`, based on the [oddsratio_to_d()] conversion, see [interpret_cohens_d()])
#'   - **OR < 1.44** - Very small
#'   - **1.44 <= OR < 2.48** - Small
#'   - **2.48 <= OR < 4.27** - Medium
#'   - **OR >= 4.27 ** - Large
#'
#' @examples
#' interpret_oddsratio(1)
#' interpret_oddsratio(c(5, 2))
#'
#' @references
#' - Cohen, J. (1988). Statistical power analysis for the behavioral sciences
#' (2nd Ed.). New York: Routledge.
#'
#' - Chen, H., Cohen, P., & Chen, S. (2010). How big is a big odds ratio?
#' Interpreting the magnitudes of odds ratios in epidemiological studies.
#' Communications in Statistics-Simulation and Computation, 39(4), 860-864.
#'
#' - Sánchez-Meca, J., Marín-Martínez, F., & Chacón-Moscoso, S. (2003).
#' Effect-size indices for dichotomized outcomes in meta-analysis. Psychological
#' methods, 8(4), 448.
#'
#' @keywords interpreters
#' @export
interpret_oddsratio <- function(OR, rules = "chen2010", log = FALSE, ...) {
  if (log) {
    OR <- exp(abs(OR))
  } else {
    OR <- exp(abs(log(OR)))
  }


  if (is.character(rules) && rules == "cohen1988") {
    d <- oddsratio_to_d(OR, log = FALSE)
    return(interpret_cohens_d(abs(d), rules = rules))
  }

  rules <- .match.rules(
    rules,
    list(
      chen2010 = rules(c(1.68, 3.47, 6.71), c("very small", "small", "medium", "large"),
        name = "chen2010", right = FALSE
      ),
      cohen1988 = NA # for correct error msg
    )
  )

  interpret(OR, rules)
}