Erratum to: On the Unidentifiability of the Fixed-Effects 3PL Model

Erratum to: PSYCHOMETRIKA, 2015, 80, 450–467 DOI 10.1007/s11336-014-9404-2

Condition 2 of Theorem 2 was incorrect in the published version. The correct condition 2 appears in this erratum.

Theorem 2

Suppose that $I\ge 3$\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$I\ge 3$$\end{document} for the fixed-effects 3PL model. If ${\omega }_1=({\alpha }_1,{\beta }_1,c_1)$\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\omega _1=(\alpha _1,\beta _1,c_1)$$\end{document} is fixed at (1, 0, 0), then

1. 1. The person parameters are identified by the observations.

2. 2. The item parameters $({\alpha }_{2:J},{\beta }_{2:J},c_{2:J})$\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\varvec{\alpha }_{2:J}, \varvec{\beta }_{2:J},\varvec{c}_{2:J})$$\end{document} are not identified by the observations.