Two-point drift check (the conventional baseline)

Pools the first and last blocks of windows, estimates each item's difficulty in both, and flags items whose robust z of the difference (median/MAD standardized) exceeds `crit`: the usual displacement check at equating time.

Usage

dw_twopoint(estimates, early = 1:5, late = NULL, crit = 2.7)

Arguments

estimates: A `dw_estimates` object.
early, late: Window indices forming the two calibrations.
crit: Robust-z criterion.

Value

Data frame: `item`, `d`, `robust_z`, `flag`.

Examples

sim <- dw_simulate(n_items = 60, n_windows = 20, mean_n = 60,
                   onset_range = c(5, 12), seed = 1)
tp <- dw_twopoint(dw_estimate(sim$responses, sim$bank))
table(flag = tp$flag, truth = sim$truth$type)
#>        truth
#> flag    abrupt gradual stable
#>   FALSE      2       6     51
#>   TRUE       0       1      0