OscatsModelNominal

OscatsModelNominal — Nominal Response Model

Synopsis

struct              OscatsModelNominal;

Object Hierarchy

  GObject
   +----OscatsModel
         +----OscatsModelNominal

Properties

  "Ncat"                     guint                 : Read / Write / Construct Only

Description

Details

struct OscatsModelNominal

struct OscatsModelNominal;

The Nominal Response IRT model: P(X=k|theta) = f_k(theta)/[1+sum_j f_j(theta)], where f_j(theta) = sum_i a_ij theta_i - b_j + sum_l d_l covariate_l, a_ij are the option discriminations for each dimension, b_j is the scaled option difficulty, and a_i0 = b_0 = 0. Responses are numbered 0, 1, ..., Ncat-1. Note that all options share the same parameters for the covariates. Distance is defined as: min_j abs(f_j(theta)).

Parameter names: Diff.j, Discr.j.DimName

References:

R. J. de Ayala (2009). The Theory and Practice of Item Response Theory. p 240.

R. J. de Ayala (1992). "The Nominal Response Model in Computerized Adaptive Testing." Applied Psychological Measurement, 16, 327-343.

R. D. Bock (1972). "Estimating item parameters and latent ability when responses are scored in two or more nominal categories." Psychometrika, 37, 29-51.

Property Details

The "Ncat" property

  "Ncat"                     guint                 : Read / Write / Construct Only

The number of response categories in the IRT model, numered 0, 1, ..., Ncat-1. The default number of categories is 3, which is also the minimum.

Allowed values: >= 3

Default value: 3