OscatsModelL2p

OscatsModelL2p — Two-Parameter Logistic (2PL) Model

Synopsis

struct              OscatsModelL2p;

Object Hierarchy

  GObject
   +----OscatsModel
         +----OscatsModelL2p

Description

Details

struct OscatsModelL2p

struct OscatsModelL2p;

The Two-Paramter Logistic IRT model: P(X=1|theta) = 1/1+exp[-(sum_i a_i theta_i -b + sum_j d_j covariate_j)], where a_i are the item discrimination for each dimension and b is the scaled item difficulty. Note that this differs from the usual IRT parameterization 1/1+exp[-a(theta-b)]. Distance is defined as: abs(sum_i a_i theta_i - b + sum_j d_j covariate_j).

Parameter names: Diff, Discr.DimName

References:

R. J. de Ayala (2009). The Theory and Practice of Item Response Theory. p 100, 277.

Mark D. Reckase (1985). "The Difficulty of Test Items That Measure More Than One Ability." Applied Psychological Measurement, 9, 401-412.