Table 3.

Fit statistics for the 21 trended anchor items in 1999, 2003, and 2007 TIMSS.

TIMSS	Unidimensional 3PL IRT model			2-Class 3PL mixture model
	−2LL	AIC	BIC	−2LL	AIC	BIC
1999	44,560	44,686	45,047	44,150	44,402	45,125
2003	89,510	89,636	90,040	87,980	88,232	89,039
2007	41,290	41,416	41,773	40,310	40,562	41,275

Estimated using MCMC with 10,000 samples and 4000 samples burn-in. The −2LL is the posterior mean of the MCMC deviance (Li et al., 2009).