. Author manuscript; available in PMC: 2015 Feb 10.

Published in final edited form as: J Sch Psychol. 2012 May 29;50(4):461–481. doi: 10.1016/j.jsp.2012.05.002

Table 3.

IRT model comparisons for the separate and combined samples.

Model	log likelihood value	-2 log likelihood test
Model	log likelihood value
		Difference^a	df	p
Florida sample (N = 1074)
Constrained	-11,255.27
One-parameter logistic model	-10,323.99	1802.58	24	<.001
Two-parameter logistic model	-10,263.25	121.47	26	<.001
Texas sample (N = 500)
Constrained	-5148.13
One-parameter logistic model	-4807.13	682.00	24	<.001
Two-parameter logistic model	-4760.36	93.58	26	<.001
Combined sample (N = 1574)
Constrained	-16,398.08
One-parameter logistic model	-15,225.78	2344.60	24	<.001
Two-parameter logistic model	-15,135.24	181.08	26	<.001

Note.

Difference from model presented immediately above.