ThreePLM: Three-Parameter Logistic Model

In exametrika: Test Theory Analysis and Biclustering

Three-Parameter Logistic Model

Description

The three-parameter logistic model is a model where the lower asymptote parameter c is added to the 2PLM

Usage

ThreePLM(a, b, c, theta)

Arguments

a	slope parameter
b	location parameter
c	lower asymptote parameter
theta	ability parameter

Value

Returns a numeric vector of probabilities between c and 1, representing the probability of a correct response given the ability level theta. The probability is calculated using the formula: P(\theta) = c + \frac{1-c}{1 + e^{-a(\theta-b)}}

exametrika documentation built on Feb. 17, 2026, 5:07 p.m.