|Statistic||Type of school1||All items2|
|Number of scaled items||20|
|Unweighted sample size||Public||132,800|
|Weighted average item score||Public||0.51|
|Weighted average polyserial||Public||0.90|
|1 Nonpublic-school sample includes only Catholic and private schools.
2 In NAEP writing assessments, each block contains only one item—a writing prompt to which students respond with a polytomously scored constructed response; therefore, the weighted alpha reliability estimate is not meaningful and does not appear in this table.
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2002 Writing Assessment.