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NAEP Technical DocumentationIRT parameters for items in the physical science scale, grade 8 science combined national and state main assessment, by item and block: 2009

Block	Item	NAEP ID	aj	bj	cj	dj1	dj2	dj3	dj4
† Not applicable; c parameters are not estimated for generalized partial credit models, and d parameters are not estimated for two-parameter or three-parameter logistic models. NOTE: For item j, aj represents the discriminatory power of the item, bj represents a location parameter related to item difficulty, cj represents the guessing parameter, and dji represents the category threshold parameter for category i. The c parameter value is exactly zero for items scaled with the two-parameter logistic model. For item j, dji may not sum to zero because of rounding. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2009 Science Assessment.
S3	4	K114001	1.03	0.19	0.31	†	†	†	†
	5	K114002	0.78	0.43	0.19	†	†	†	†
	7	K113201	0.32	-0.75	†	2.44	-1.96	-0.48	†
	10	K113602	0.06	8.25	0.16	†	†	†	†
	11	K113603	0.42	0.69	0.08	†	†	†	†
	15	K134201	0.46	-0.06	†	-0.37	-0.11	0.48	†
S4	2	K114601	0.43	0.17	†	-0.25	0.46	-0.21	0.00
	8	K116701	1.45	1.14	0.32	†	†	†	†
	10	K118901	1.06	-0.51	0.33	†	†	†	†
	11	K122402	0.30	1.67	†	-0.77	2.29	-1.53	0.00
	14	K122001	1.22	0.62	0.27	†	†	†	†
S5	2	K120601	1.65	1.72	0.29	†	†	†	†
	11	K120901	0.79	0.47	0.21	†	†	†	†
	12	K121401	1.61	0.63	0.55	†	†	†	†
	13	K121402	1.24	0.21	0.38	†	†	†	†
	14	K121403	3.15	1.39	0.11	†	†	†	†
S6	3	K124601	0.61	1.79	0.29	†	†	†	†
	6	K154901	0.58	0.58	0.22	†	†	†	†
	8	K125001	0.81	1.51	0.31	†	†	†	†
	9	K125002	0.90	0.83	0.28	†	†	†	†
	10	K125003	0.34	0.96	†	0.82	-0.82	†	†
	12	K155101	1.06	1.49	0.20	†	†	†	†
	13	K155201	0.94	0.38	0.23	†	†	†	†
S7	3	K155401	0.65	-0.06	0.16	†	†	†	†
	9	K123901	0.48	0.77	†	1.40	1.61	-0.52	-2.50
	15	K110801	1.00	1.65	0.25	†	†	†	†
	16	K110101	1.58	1.54	0.33	†	†	†	†
S8	3	K111901	0.86	1.57	0.46	†	†	†	†
	6	K112401	0.61	1.30	†	-0.55	-2.35	2.90	†
	9	K155601	0.27	2.65	†	-1.84	1.51	2.15	-1.81
	10	K117201	0.73	0.41	0.30	†	†	†	†
	11	K117202	0.54	-0.27	†	†	†	†	†
	15	K112901	0.87	1.62	0.25	†	†	†	†
	17	K112701	0.54	0.33	0.20	†	†	†	†
S9	4	K114901	1.29	0.43	0.25	†	†	†	†
	5	K1560CL	0.20	2.35	†	1.28	-0.89	-0.39	†
	10	K115301	1.15	-0.27	0.32	†	†	†	†
S10	1	K116401	0.76	-0.54	0.30	†	†	†	†
	9	K110901	0.60	1.67	†	0.06	-0.06	†	†
	11	K116001	1.15	1.75	0.26	†	†	†	†
	12	K116002	0.55	0.25	†	0.19	-0.19	†	†
	17	K115701	0.66	-0.48	0.24	†	†	†	†
S11	2	K123201	0.88	0.76	0.31	†	†	†	†
	4	K156701	0.91	1.87	0.20	†	†	†	†
S12	2	K156801	1.24	0.64	0.18	†	†	†	†
	8	K157001	0.68	1.02	†	1.28	-1.28	†	†
	9	K119505	1.06	0.25	†	†	†	†	†
	11	K123401	0.62	0.42	†	0.25	-0.41	0.16	†

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