Extract Thurstonian IRT Parameters from a lavaan-Fitted Model

Extracts and aligns the core parameter blocks needed for Thurstonian IRT scoring from a fitted lavaan object (as stored in fit_lavaan_obj$fit). The returned pieces are aligned to the row order of Lambda, which is critical for correct downstream scoring.

Specifically, this function returns:

Lambda: factor loading matrix.
theta_diag: residual variances (diagonal of theta), reordered to rownames(Lambda) when names are available.
tau: thresholds from tau, reordered to rownames(Lambda) and with row suffixes like "|t1" removed.
nu: indicator intercepts; defaults to zero when unavailable.
Psi: latent covariance matrix (psi).

Usage

extract_tirt_params(fit_lavaan_obj)

Arguments

fit_lavaan_obj: A fitted object containing a lavaan fit in $fit. For example, an object produced by a wrapper that stores a lavaan model under fit_lavaan_obj$fit.

Value

A named list with elements: Lambda, theta_diag, tau, nu, and Psi.

Details

Threshold rows in lavaan are often named like "item|t1". This function strips everything after "|" before matching thresholds to indicators.

Examples

library(thurstonianIRT)
#> Loading required package: Rcpp
data("triplets")
# define the blocks of items
blocks <-
  set_block(c("i1", "i2", "i3"), traits = c("t1", "t2", "t3"),
            signs = c(1, 1, 1)) +
  set_block(c("i4", "i5", "i6"), traits = c("t1", "t2", "t3"),
            signs = c(-1, 1, 1)) +
  set_block(c("i7", "i8", "i9"), traits = c("t1", "t2", "t3"),
            signs = c(1, 1, -1)) +
  set_block(c("i10", "i11", "i12"), traits = c("t1", "t2", "t3"),
            signs = c(1, -1, 1))
# generate the data to be understood by 'thurstonianIRT'
triplets_long <- make_TIRT_data(
  data = triplets, blocks = blocks, direction = "larger",
  format = "pairwise", family = "bernoulli", range = c(0, 1)
)
# fit the data using lavaan
fit <- fit_TIRT_lavaan(triplets_long)
pars <- extract_tirt_params(fit)