NAEP Analysis and Scaling → Initial Activities → Classical Item Analysis → Block-Level Descriptive Statistics as Defined After Scaling, Grade 8 Mathematics Combined National and State Main Assessment, by Public and Nonpublic School Sessions: 2009

NAEP Technical DocumentationBlock-level descriptive statistics as defined after scaling, grade 8 mathematics combined national and state main assessment, by public and nonpublic school sessions: 2009

Statistic	Type of School1	Block M3	Block M4	Block M5	Block M6	Block M7	Block M8	Block M9	Block M10	Block M11	Block M12
† Not applicable. 1 Nonpublic school sample includes only Private and Catholic schools. 2 The "Weighted proportion of students attempting last item" is equal to 1 - (Percent not responding to last item /100). 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	†	15	14	18	16	16	15	15	16	17	17
Unweighted sample size	Public	31,200	31,000	31,100	31,100	31,000	31,200	31,200	31,400	31,300	31,500
	Nonpublic	600	600	600	600	600	600	600	600	600	600
Weighted average item score	Public	0.46	0.44	0.59	0.52	0.47	0.51	0.49	0.53	0.45	0.49
	Nonpublic	0.53	0.49	0.65	0.58	0.53	0.59	0.57	0.61	0.51	0.55
Weighted average polyserial	Public	0.63	0.66	0.62	0.65	0.58	0.62	0.65	0.62	0.58	0.59
	Nonpublic	0.63	0.64	0.62	0.62	0.56	0.62	0.63	0.58	0.54	0.58
Weighted alpha reliability	Public	0.77	0.79	0.80	0.80	0.73	0.78	0.77	0.78	0.78	0.77
	Nonpublic	0.77	0.77	0.78	0.77	0.71	0.77	0.74	0.73	0.74	0.75
Weighted proportion of students attempting last item2	Public	0.92	0.94	0.87	0.93	0.96	0.96	0.96	0.98	0.88	0.97
	Nonpublic	0.94	0.98	0.94	0.97	0.99	0.98	0.98	0.99	0.92	0.98

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