draft

DESCRIPTION

@@ -1,7 +1,7 @@
 Type: Package
 Package: performance
 Title: Assessment of Regression Models Performance
-Version: 0.10.8.9
+Version: 0.10.8.10
 Authors@R: 
     c(person(given = "Daniel",
              family = "Lüdecke",

NAMESPACE

@@ -136,6 +136,8 @@ S3method(logLik,iv_robust)
 S3method(logLik,ivreg)
 S3method(logLik,plm)
 S3method(logLik,svycoxph)
+S3method(mcdonalds_omega,data.frame)
+S3method(mcdonalds_omega,matrix)
 S3method(model_performance,Arima)
 S3method(model_performance,BFBayesFactor)
 S3method(model_performance,DirichletRegModel)
@@ -542,6 +544,7 @@ export(item_reliability)
 export(item_split_half)
 export(looic)
 export(mae)
+export(mcdonalds_omega)
 export(model_performance)
 export(mse)
 export(multicollinearity)

NEWS.md

@@ -1,5 +1,9 @@
 # performance 0.10.9
 
+## New functions
+
+* `mcdonalds_omega()` to calculate McDonald's Omega for a scale.
+
 ## Changes
 
 * `r2()` for models of class `glmmTMB` without random effects now returns the

R/mcdonalds_omega.r

@@ -0,0 +1,55 @@
+#' @title McDonald's Omega for Items or Scales
+#' @name mcdonalds_omega
+#'
+#' @description Compute various measures of internal consistencies
+#'    for tests or item-scales of questionnaires.
+#'
+#' @param x A matrix or a data frame.
+#' @param ... Currently not used.
+#'
+#' @return The McDonald's Omega value for `x`.
+#'
+#' @details The McDonald's Omega value for `x`. A value closer to 1
+#'    indicates greater internal consistency, where usually following
+#'    rule of thumb is applied to interpret the results:
+#'    \ifelse{html}{\out{&alpha;}}{\eqn{\alpha}{alpha}} < 0.5 is unacceptable,
+#'    0.5 < \ifelse{html}{\out{&alpha;}}{\eqn{\alpha}{alpha}} < 0.6 is poor,
+#'    0.6 < \ifelse{html}{\out{&alpha;}}{\eqn{\alpha}{alpha}} < 0.7 is questionable,
+#'    0.7 < \ifelse{html}{\out{&alpha;}}{\eqn{\alpha}{alpha}} < 0.8 is acceptable,
+#'    and everything > 0.8 is good or excellent.
+#'
+#' @references Bland, J. M., and Altman, D. G. Statistics notes: Cronbach's
+#'   alpha. BMJ 1997;314:572. 10.1136/bmj.314.7080.572
+#'
+#' @examples
+#' data(mtcars)
+#' x <- mtcars[, c("cyl", "gear", "carb", "hp")]
+#' mcdonalds_omega(x)
+#' @export
+mcdonalds_omega <- function(x, ...) {
+  UseMethod("mcdonalds_omega")
+}
+
+
+#' @export
+mcdonalds_omega.data.frame <- function(x, verbose = TRUE, ...) {
+  # remove missings
+  .data <- stats::na.omit(x)
+
+  # we need at least two columns for Cronach's Alpha
+  if (is.null(ncol(.data)) || ncol(.data) < 2) {
+    if (verbose) {
+      insight::format_warning("Too few columns in `x` to compute McDonald's Omega.")
+    }
+    return(NULL)
+  }
+
+  # Compute Cronbach's Alpha
+  dim(.data)[2] / (dim(.data)[2] - 1) * (1 - sum(apply(.data, 2, stats::var)) / stats::var(rowSums(.data)))
+}
+
+
+#' @export
+mcdonalds_omega.matrix <- function(x, verbose = TRUE, ...) {
+  mcdonalds_omega(as.data.frame(x), verbose = verbose, ...)
+}

_pkgdown.yaml

@@ -24,6 +24,7 @@ reference:
     contents:
       - check_itemscale
       - cronbachs_alpha
+      - mcdonalds_omega
       - starts_with("item_")
 
   - title: "Comparing and Testing Models"