NAEP Analysis and Scaling → Initial Activities → Classical Item Analysis → Overall Descriptive Statistics for Items as Defined After Scaling, Grade 8 Mathematics Combined National and State Main Assessment: 2009

NAEP Technical DocumentationOverall descriptive statistics for items as defined after scaling, grade 8 mathematics combined national and state main assessment: 2009

Statistic	Item type	Block M3	Block M4	Block M5	Block M6	Block M7	Block M8	Block M9	Block M10	Block M11	Block M12
† 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 Mathematics Assessment.
Number of scaled items	Total	15	14	18	16	16	15	15	16	17	17
	Multiple choice	11	11	9	13	11	11	10	13	12	14
	Dichtomously scored constructed response	2	0	4	1	1	0	2	2	0	1
	Polytomously scored constructed response	2	3	5	2	4	4	3	1	5	2
Unweighted sample size	†	32,300	32,100	32,200	32,200	32,100	32,300	32,300	32,500	32,400	32,600
Weighted average item score	†	0.47	0.44	0.60	0.52	0.48	0.51	0.50	0.54	0.46	0.50
Weighted average polyserial	†	0.63	0.66	0.62	0.64	0.58	0.62	0.65	0.62	0.57	0.59
Weighted alpha reliability	†	0.77	0.79	0.80	0.80	0.73	0.78	0.77	0.78	0.78	0.77
Weighted proportion of students attempting last item1	†	0.92	0.95	0.88	0.93	0.97	0.97	0.97	0.98	0.89	0.97

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