discrpar_longitudinal_grmtree: Extract Discrimination Parameters from Longitudinal GRM Tree

In grmtree: Recursive Partitioning for Graded Response Models

Extract Discrimination Parameters from Longitudinal GRM Tree

Description

Extracts discrimination (slope) parameters for each unique item from all terminal nodes of a longitudinal GRM tree. The longitudinal model uses columns "a1" (T1 loading) and "a2" (T2 loading); this function extracts the T1 discrimination since a1 = a2 under the equality constraint.

Usage

discrpar_longitudinal_grmtree(object, node = NULL, clean_names = TRUE, ...)

Arguments

object	A longitudinal_grmtree object.
node	Optional vector of node IDs. If NULL (default), extracts from all terminal nodes.
clean_names	Logical. If TRUE (default), clean item names.
...	Additional arguments (currently unused).

Value

A data.frame with columns:

Node

Terminal node ID

Item

Item name

Discrimination

Discrimination parameter (a1 from T1 items)

See Also

longitudinal_grmtree for Phase 1 (tree fitting), threshpar_longitudinal_grmtree for extracting threshold parameters for longitudinal GRMTree, itempar_longitudinal_grmtree for extracting item parameters for longitudinal GRMTree

Examples

library(grmtree)

# Load the synthetic longitudinal data
data("grmtree_long_data", package = "grmtree")

  # Prepare the wide-format response matrix
  items_t1 <- c("MOS_Listen", "MOS_Info", "MOS_Advice_Crisis", "MOS_Confide",
                "MOS_Advice_Want", "MOS_Fears", "MOS_Personal", "MOS_Understand")
  ld <- prepare_longitudinal_data(
    data = grmtree_long_data,
    items_t1 = items_t1,
    items_t2 = paste0(items_t1, "_year1"),
    covariates = c("sex", "age", "residency", "job",
                   "education", "comorbidity_count", "ever_smoker")
  )

  # Phase 1: fit the longitudinal GRM tree
  ltree <- longitudinal_grmtree(
    resp_wide ~ sex + age + residency + job +
      education + comorbidity_count + ever_smoker,
    data = ld, n_items = 8,
    control = grmtree.control(minbucket = 200)
  )

  # Print the discrimination parameters
  discr <- discrpar_longitudinal_grmtree(ltree)
print(discr)

grmtree documentation built on Sept. 2, 2026, 1:07 a.m.