easystats / easystats/modelbased

Formatting inconsistency in estimate_grouplevel() with a categorical predictor

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Bug :bug: Consistency :green_apple: :apple:
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Description

When extracting random effects from an lmer model using estimate_grouplevel(), the formatting of factor levels in the Parameter column is inconsistent. The first instance of a factor's random slope gets cleaned up nicely (e.g., treatment [1]), but all subsequent rows for that same parameter revert to the raw lme4 naming convention (e.g., treatment1).

library(lme4)
#> Loading required package: Matrix
library(easystats)
#> # Attaching packages: easystats 0.7.5
#> ✔ bayestestR  0.17.0   ✔ correlation 0.8.8 
#> ✔ datawizard  1.3.0    ✔ effectsize  1.0.1 
#> ✔ insight     1.4.6    ✔ modelbased  0.14.0
#> ✔ performance 0.16.0   ✔ parameters  0.28.3
#> ✔ report      0.6.3    ✔ see         0.13.0

# Prepare built-in data with a 0/1 categorical predictor
dat <- sleepstudy |> 
  dplyr::mutate(treatment = factor(ifelse(Days > 4, "1", "0")))

# Fit a model with a random slope for the factor
fit <- lmer(Reaction ~ treatment + (1 + treatment | Subject), data = dat)

# Extract random effects
# Notice Subject 308 gets "treatment [1]" while 309+ get "treatment1"
estimate_grouplevel(fit, type = "random")
#> Group   | Level | Parameter     | Coefficient |    SE |           95% CI
#> ------------------------------------------------------------------------
#> Subject | 308   | (Intercept)   |       21.70 | 10.38 | [  1.36,  42.04]
#> Subject | 308   | treatment [1] |       42.41 | 14.18 | [ 14.61,  70.20]
#> Subject | 309   | (Intercept)   |      -55.24 | 10.38 | [-75.58, -34.90]
#> Subject | 309   | treatment1    |      -44.64 | 14.18 | [-72.44, -16.85]
#> Subject | 310   | (Intercept)   |      -45.89 | 10.38 | [-66.23, -25.55]
#> Subject | 310   | treatment1    |      -33.27 | 14.18 | [-61.06,  -5.48]
#> Subject | 330   | (Intercept)   |       11.64 | 10.38 | [ -8.70,  31.98]
#> Subject | 330   | treatment1    |      -19.84 | 14.18 | [-47.64,   7.95]
#> Subject | 331   | (Intercept)   |       16.66 | 10.38 | [ -3.68,  37.00]
#> Subject | 331   | treatment1    |      -18.86 | 14.18 | [-46.66,   8.93]
#> Subject | 332   | (Intercept)   |        4.69 | 10.38 | [-15.65,  25.03]
#> Subject | 332   | treatment1    |        7.72 | 14.18 | [-20.08,  35.51]
#> Subject | 333   | (Intercept)   |       13.59 | 10.38 | [ -6.75,  33.93]
#> Subject | 333   | treatment1    |        4.51 | 14.18 | [-23.28,  32.31]
#> Subject | 334   | (Intercept)   |       -4.43 | 10.38 | [-24.77,  15.91]
#> Subject | 334   | treatment1    |        4.34 | 14.18 | [-23.45,  32.14]
#> Subject | 335   | (Intercept)   |      -22.23 | 10.38 | [-42.57,  -1.89]
#> Subject | 335   | treatment1    |      -51.99 | 14.18 | [-79.78, -24.19]
#> Subject | 337   | (Intercept)   |       49.50 | 10.38 | [ 29.16,  69.84]
#> Subject | 337   | treatment1    |       45.91 | 14.18 | [ 18.11,  73.70]
#> Subject | 349   | (Intercept)   |      -20.23 | 10.38 | [-40.58,   0.11]
#> Subject | 349   | treatment1    |        1.49 | 14.18 | [-26.30,  29.29]
#> Subject | 350   | (Intercept)   |       -1.37 | 10.38 | [-21.72,  18.97]
#> Subject | 350   | treatment1    |       38.02 | 14.18 | [ 10.22,  65.81]
#> Subject | 351   | (Intercept)   |       -1.65 | 10.38 | [-21.99,  18.69]
#> Subject | 351   | treatment1    |      -14.84 | 14.18 | [-42.63,  12.96]
#> Subject | 352   | (Intercept)   |       28.95 | 10.38 | [  8.61,  49.29]
#> Subject | 352   | treatment1    |       12.62 | 14.18 | [-15.17,  40.42]
#> Subject | 369   | (Intercept)   |        5.29 | 10.38 | [-15.05,  25.63]
#> Subject | 369   | treatment1    |        3.26 | 14.18 | [-24.53,  31.06]
#> Subject | 370   | (Intercept)   |      -15.14 | 10.38 | [-35.48,   5.20]
#> Subject | 370   | treatment1    |       24.26 | 14.18 | [ -3.53,  52.06]
#> Subject | 371   | (Intercept)   |        0.73 | 10.38 | [-19.61,  21.07]
#> Subject | 371   | treatment1    |       -9.96 | 14.18 | [-37.75,  17.84]
#> Subject | 372   | (Intercept)   |       13.44 | 10.38 | [ -6.90,  33.78]
#> Subject | 372   | treatment1    |        8.86 | 14.18 | [-18.94,  36.65]

Created on 2026-03-01 with reprex v2.1.1

Expected Behavior

The Parameter column should apply the factor [level] formatting consistently across all grouping levels rather than just the first one.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the estimate_grouplevel() entry point and reproduce the issue using the lmer model and categorical treatment predictor shown in the report. Trace how the Parameter column is formatted across grouping levels. Done means every random-slope row uses consistent factor-level formatting, and the reproducer output no longer mixes bracketed and raw names.

Written by the indexing model from the issue text.

Assessment

Tech stack
r
Domain
data
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
50/100

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