Fix term labels in check_collinearity() for brms models with 0 + Intercept syntax

DESCRIPTION

@@ -1,7 +1,7 @@
 Type: Package
 Package: performance
 Title: Assessment of Regression Models Performance
-Version: 0.18.2.4
+Version: 0.18.2.5
 Authors@R:
     c(person(given = "Daniel",
              family = "Lüdecke",

NEWS.md

@@ -2,6 +2,10 @@
 
 ## Bug fixes
 
+* `check_collinearity()` now labels terms correctly for *brms* models that use
+  the `0 + Intercept` formula syntax. Before, each VIF was shown under the name
+  of the previous term and the last term was missing (#417).
+
 * `check_model()` now correctly returns the random-effects normality panel for
   mixed models that specify random slopes using split terms such as
   `(1 | group) + (0 + slope | group)` (including `||` expansions, #845).

R/check_collinearity.R

@@ -447,7 +447,7 @@
 }
 
 
 .check_collinearity <- function(x, component, ci = 0.95, verbose = TRUE) {
   v <- .safe(insight::get_varcov(x, component = component, verbose = FALSE))
 
   # fix class for fixest, which returns a "fixest_vcov" here
@@ -537,7 +537,7 @@
           "Model matrix is rank deficient. VIFs may not be sensible.",
           paste0(
             "The following coefficients have VIF = Inf / tolerance = 0: ",
             paste0(na_cols, collapse = ", ")
           )
         )
       } else {
@@ -574,6 +574,12 @@
     model_terms <- labels(stats::terms(f[[component]]))
   }
 
+  # brms formulas like `y ~ 0 + Intercept + x` list "Intercept" as a term, but
+  # it is the model's intercept, which is not part of the term assignment
+  if (inherits(x, "brmsfit")) {
+    model_terms <- setdiff(model_terms, "Intercept")
+  }
+
   if ("instruments" %in% names(f)) {
     model_terms <- unique(c(model_terms, labels(stats::terms(f[["instruments"]]))))
   }
@@ -592,7 +598,7 @@
     return(NULL)
   }
 
   R <- stats::cov2cor(v)
   detR <- det(R)
 
   result <- vector("numeric")

tests/testthat/test-check_collinearity.R

@@ -78,7 +78,7 @@
     .package = "insight"
   )
   testthat::local_mocked_bindings(
     model.matrix = function(...) stop("rebuild failed"),
     .package = "stats"
   )
   expect_null(
@@ -216,9 +216,9 @@
   expect_warning(expect_message(ccoW <- check_collinearity(aW))) # nolint
   expect_message(ccoB <- check_collinearity(aB), regexp = NA) # nolint
 
   expect_identical(nrow(ccoM), 15L)
   expect_identical(nrow(ccoW), 3L)
   expect_identical(nrow(ccoB), 3L)
 
   suppressWarnings(suppressMessages({
     aM <- afex::aov_car(
@@ -244,8 +244,8 @@
   expect_warning(expect_message(ccoW <- check_collinearity(aW))) # nolint
   expect_message(ccoB <- check_collinearity(aB), regexp = NA) # nolint
 
   expect_identical(nrow(ccoM), 15L)
   expect_identical(nrow(ccoW), 3L)
   expect_identical(nrow(ccoB), 3L)
 })
 
@@ -487,3 +487,26 @@
   })
   expect_identical(out1$VIF, out2$VIF)
 })
+
+
+test_that("check_collinearity, brms with 0 + Intercept syntax", {
+  skip_on_cran()
+  skip_if_not_installed("brms")
+  m <- suppressMessages(suppressWarnings(brms::brm(
+    mpg ~ 0 + Intercept + cyl + disp + hp,
+    data = mtcars,
+    chains = 1,
+    iter = 500,
+    refresh = 0,
+    seed = 123,
+    silent = 2
+  )))
+  expect_silent({
+    out <- check_collinearity(m, ci = NULL)
+  })
+  expect_identical(out$Term, c("cyl", "disp", "hp"))
+  # VIFs for slopes, computed from the posterior correlation matrix
+  v <- insight::get_varcov(m)
+  R <- stats::cov2cor(v[-1, -1])
+  expect_equal(out$VIF, unname(diag(solve(R))), tolerance = 1e-6)
+})