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NAEP Technical DocumentationIRT parameters for items in the life 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	6	K113401	0.31	0.78	†	-0.17	-0.14	2.66	-2.34
	12	K113001	1.19	-0.11	0.34	†	†	†	†
	13	K113801	0.65	0.17	0.31	†	†	†	†
	17	K113501	0.59	0.37	0.26	†	†	†	†
S4	1	K117801	1.27	-0.62	0.37	†	†	†	†
	4	K122301	0.77	0.71	0.23	†	†	†	†
	5	K122302	1.21	0.51	0.42	†	†	†	†
	6	K122303	1.27	1.59	0.29	†	†	†	†
	7	K122304	1.85	0.88	0.25	†	†	†	†
	13	K122801	0.71	1.45	†	0.56	-0.56	†	†
	16	K125201	0.35	0.39	†	0.10	0.80	-1.56	0.66
S5	3	K154501	0.95	0.08	0.24	†	†	†	†
	9	K118501	0.52	1.17	†	1.32	-0.08	-1.25	†
	10	K154601	0.50	0.43	†	0.79	-0.79	†	†
	15	K154701	0.67	1.25	†	2.91	-0.35	-0.51	-2.04
	16	K154801	0.94	-0.69	0.27	†	†	†	†
	18	K120501	1.32	-0.02	0.27	†	†	†	†
S6	2	K124501	1.51	0.79	0.27	†	†	†	†
	4	K123801	0.66	0.58	†	0.42	0.01	-0.43	†
	5	K123802	0.42	0.42	†	0.68	-0.68	†	†
	11	K155001	1.50	-0.26	0.35	†	†	†	†
	16	K155301	1.52	0.66	0.39	†	†	†	†
S7	2	K117401	1.28	0.81	0.13	†	†	†	†
	6	K110601	1.00	-0.92	0.28	†	†	†	†
	12	K110501	0.69	1.39	†	1.02	-1.02	†	†
	13	K121001	0.88	1.48	†	0.30	-0.30	†	†
	14	K1210CL	0.41	0.49	†	-0.80	1.84	-1.04	†
S8	1	K112801	0.92	-0.61	0.29	†	†	†	†
	7	K112001	2.02	0.62	0.19	†	†	†	†
	8	K119701	2.05	0.63	0.28	†	†	†	†
	14	K111601	0.68	0.24	0.17	†	†	†	†
	16	K155801	1.26	-0.30	0.27	†	†	†	†
	18	K155901	0.61	0.10	0.27	†	†	†	†
S9	2	K114401	1.35	0.60	0.20	†	†	†	†
	8	K114802	0.59	0.26	†	-0.34	0.34	†	†
	9	K114801	0.36	1.94	†	-1.26	2.59	-1.33	†
	12	K124102	0.36	0.56	†	-1.33	1.92	-0.59	†
S10	5	K115801	0.87	0.02	0.27	†	†	†	†
	6	K1158CL	0.72	-1.89	†	0.78	-0.78	†	†
	7	K1564CL	0.80	0.16	†	1.11	-1.11	†	†
	10	K116101	0.43	1.22	†	0.89	2.07	-1.45	-1.51
S11	3	K119201	1.08	0.85	0.34	†	†	†	†
	10	K117001	0.55	1.01	†	0.48	-0.48	†	†
	11	K1170CL	0.45	1.52	†	-0.02	-0.14	0.16	†
	12	K117005	0.73	-0.86	0.32	†	†	†	†
	13	K117006	1.43	1.05	0.29	†	†	†	†
S12	7	K123301	0.75	0.07	†	†	†	†	†
	12	K112601	0.74	2.05	†	0.79	-0.79	†	†

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