NAEP TECHNICAL DOCUMENTATIONOverall descriptive statistics for items as defined after scaling, grade 8 mathematics combined national and state assessments, by block: 2011

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. NOTE: The "weighted average item score" of polytomous items are standardized to have a scale of 0 to 1 so they are comparable to dichotomously scored items. The "weighted proportion of students attempting last item" is equal to 1 (percent not responding to last item /100). 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), 2011 Mathematics Assessment.
Number of scaled items	Total	15	14	15	16	16	15	15	15	17	17
	Multiple choice	11	11	11	13	11	11	10	11	12	14
	Dichtomously scored constructed response	2	0	1	1	1	0	2	0	0	1
	Polytomously scored constructed response	2	3	3	2	4	4	3	4	5	2
Unweighted sample size	†	35,000	35,000	35,100	35,100	35,000	34,800	35,100	35,000	35,100	35,100
Weighted average item score	†	.48	.45	.46	.53	.48	.51	.50	.54	.47	.51
Weighted average polyserial	†	.62	.65	.53	.64	.58	.62	.65	.61	.58	.60
Weighted alpha reliability	†	.76	.78	.70	.80	.73	.78	.77	.76	.78	.78
Weighted proportion of students attempting last item	†	.91	.95	.84	.92	.96	.96	.96	.87	.87	.96

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