docs

Author: strengejacke

R/estimate_contrasts.R

@@ -33,8 +33,12 @@
 #'   [this website](https://marginaleffects.com/bonus/hypothesis.html) and
 #'   section _Comparison options_ below.
 #'   * String: One of `"pairwise"`, `"reference"`, `"sequential"`, `"meandev"`
-#'     `"meanotherdev"`, `"poly"`, `"helmert"`, or `"trt_vs_ctrl"`. To test
-#'     multiple hypotheses jointly (usually used for factorial designs),
+#'     `"meanotherdev"`, `"poly"`, `"helmert"`, `"slope"` or `"trt_vs_ctrl"`.
+#'     The `"slope"` option calculcates contrasts between average slopes and can
+#'     also be used to calculate "context" effects, which is the difference of
+#'     within- and between-effects (see
+#'     https://statisticalhorizons.com/between-within-contextual-effects/). To
+#'     test multiple hypotheses jointly (usually used for factorial designs),
 #'     `comparison` can also be `"joint"`. In this case, use the `test` argument
 #'     to specify which test should be conducted: `"F"` (default) or `"Chi2"`.
 #'   * String: Special string options are `"inequality"`, `"inequality_ratio"`,

R/format.R

@@ -16,7 +16,7 @@ format.estimate_contrasts <- function(
   }
   # change parameter name for context effects
   if (isTRUE(attributes(x)$context_effects)) {
-    x$Parameter <- "Context effect"
+    x$Parameter <- "Average slope"
   }
 
   # don't print columns of adjusted_for variables

R/get_inequalitycontrasts.R

@@ -260,6 +260,10 @@
       return(out)
     }
   }
+  # handle special value: contrasting average slopes (context effects)
+  if (identical(comparison, "slope")) {
+    comparison <- "context"
+  }
   comparison
 }
 

R/get_marginalcontrasts.R

@@ -108,7 +108,7 @@ get_marginalcontrasts <- function(
     # sanity check - contrast for slopes only makes sense when we have a "by" argument
     if (is.null(my_args$by)) {
       insight::format_error(
-        "Please specify the `by` argument to calculate contrasts of slopes."
+        "Please specify the `by` argument to calculate contrasts of slopes. If you want to calculate the average contrast between two slopes, use `comparison = \"slope\"` instead."
       )
     }
     # call slopes with hypothesis argument

man/estimate_contrasts.Rd

@@ -37,6 +37,13 @@ test_that("estimate_contrast, context effects, glm", {
   )
   expect_equal(out$Estimate, exp(b[1] - b[2]), tolerance = 1e-4, ignore_attr = TRUE)
 
+  out <- modelbased::estimate_contrasts(
+    m,
+    c("bill_len_between", "bill_len_within"),
+    comparison = "slope"
+  )
+  expect_equal(out$Estimate, exp(b[1] - b[2]), tolerance = 1e-4, ignore_attr = TRUE)
+
   out <- modelbased::estimate_contrasts(
     m,
     c("bill_len_between", "bill_len_within"),