|Statistic||Item type||Block C3||Block C4||Block C5||Block C6||Block C7||Block C8|
|Number of scaled items||Total||15||15||15||14||15||14|
|Dichotomously scored constructed response||0||1||0||1||0||0|
|Polytomously scored constructed response||4||3||3||3||4||3|
|Unweighted sample size||†||2,300||2,400||2,300||2,300||2,300||2,300|
|Weighted average item score||†||0.52||0.47||0.49||0.57||0.53||0.53|
|Weighted average polyserial||†||0.52||0.53||0.55||0.53||0.56||0.49|
|Weighted alpha reliability||†||0.69||0.69||0.72||0.68||0.75||0.65|
|Weighted proportion of students attempting last item1||†||0.88||0.90||0.88||0.87||0.81||0.91|
|† 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), 2006 Civics Assessment.