|Number of scaled items||20|
|Dichotomously scored constructed response||0|
|Polytomously scored constructed response||20|
|Unweighted sample size||18,500|
|Weighted average item score||.57|
|Weighted average polyserial||.90|
|Weighted alpha reliability||†|
|† 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.
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2002 Writing Assessment.