Table 3. Model comparison between the unconstrained (2PL) and constrained (1PL) graded response models.

Model	BIC	logLik	Δχ2	df	p value
Constrained (1PL)	5,080	−2,486
Unconstrained (2PL)	5,045	−2,459	54	3	<0.001

Note:

Abbreviations: BIC, Bayesian Information Criterion; logLik, Log Likelihood; LRT, Likelihood Ratio Test; DF, degrees of freedom.