Get Item Slip (False Negative) Probability — calc_item_slip

Calculates the probability a student answers this item INCORRECTLY despite possessing all required skills (True Master).

Usage

calc_item_slip_prob(results, item)

Arguments

results: The full pgdcm results list object.
item: A string item ID or integer index.

Value

A list containing the target item, posterior mean slip probability, and 95

Semantic Interpretation

This is mathematically identical to (1 - True Mastery Probability). * **High Value (> 0.3)**: A high slip rate indicates the item is tricky, wordy, or prone to careless computational errors by students who otherwise completely understand the math. * **Low Value (< 0.1)**: Excellent item reliability. Masters almost never get this wrong by accident.