LogisticModel: Four-Parameter Logistic Model

In exametrika: Test Theory Analysis and Biclustering

Four-Parameter Logistic Model

Description

The four-parameter logistic model is a model where one additional parameter d, called the upper asymptote parameter, is added to the 3PLM.

Usage

LogisticModel(a = 1, b, c = 0, d = 1, theta)

Arguments

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

Value

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

exametrika documentation built on Aug. 21, 2025, 5:27 p.m.