NAEP Analysis and Scaling → Initial Activities → Classical Item Analysis → Overall Descriptive Statistics for Items as Defined After Scaling, Grade 12 Science Combined National and State Main Assessment: 2009

NAEP Technical DocumentationOverall descriptive statistics for items as defined after scaling (univariate scale), grade 12 science combined national and state main assessment: 2009

Statistic	Item type	Block S3	Block S4	Block S5	Block S6	Block S7	Block S8	Block S9	Block S10	Block S11	Block S12	Block S13
† Not applicable. 1 The "Weighted proportion of students attempting last item" is equal to 1 - (Percent not responding to last item /100). NOTE: Univariate scale. Item statistics in this table are described on the page Blocks of Items. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2009 Science Assessment.
Number of scaled items	Total	17	17	16	17	16	17	18	16	16	14	15
	Multiple choice	11	12	11	12	10	11	12	11	11	9	10
	Dichtomously scored constructed response	1	1	3	3	2	1	1	1	1	†	†
	Polytomously scored constructed response	5	4	2	2	4	5	5	4	4	5	5
Unweighted sample size	†	2,000	2,000	2,000	2,000	2,000	2,100	2,100	2,000	2,000	2,000	2,000
Weighted average item score	†	0.47	0.44	0.41	0.41	0.46	0.45	0.41	0.42	0.46	0.42	0.40
Weighted average polyserial	†	0.56	0.56	0.53	0.53	0.59	0.58	0.59	0.57	0.57	0.54	0.54
Weighted alpha reliability	†	0.75	0.74	0.67	0.70	0.77	0.78	0.79	0.72	0.71	0.65	0.71
Weighted proportion of students attempting last item1	†	0.91	0.91	0.91	0.91	0.96	0.95	0.93	0.96	0.96	0.96	0.90

Overall descriptive statistics for items as defined after scaling (content area scale), grade 12 science combined national and state main assessment: 2009

Statistic	Item type	Block S3	Block S4	Block S5	Block S6	Block S7	Block S8	Block S9	Block S10	Block S11	Block S12	Block S13
† Not applicable. 1 The "Weighted proportion of students attempting last item" is equal to 1 - (Percent not responding to last item /100). NOTE: Item statistics in this table are described on the page Blocks of Items. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2009 Science Assessment.
Number of scaled items	Total	17	17	17	17	16	17	18	16	16	15	15
	Multiple choice	11	12	12	12	10	11	12	11	11	10	10
	Dichtomously scored constructed response	1	1	2	1	2	†	†	1	1	†	†
	Polytomously scored constructed response	5	4	3	4	4	6	6	4	4	5	5
Unweighted sample size	†	2,000	2,000	2,000	2,000	2,000	2,100	2,100	2,000	2,000	2,000	2,000
Weighted average item score	†	0.46	0.44	0.41	0.39	0.46	0.45	0.41	0.41	0.46	0.40	0.40
Weighted average polyserial	†	0.56	0.56	0.51	0.53	0.59	0.58	0.58	0.57	0.56	0.53	0.54
Weighted alpha reliability	†	0.75	0.74	0.66	0.71	0.77	0.78	0.79	0.73	0.71	0.65	0.71
Weighted proportion of students attempting last item1	†	0.91	0.91	0.91	0.91	0.96	0.95	0.93	0.96	0.96	0.96	0.90

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