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NAEP Assessment Sample Design → NAEP 2008 Sample Design → 2008 Long-Term Trend (LTT) Assessment Sample Design

NAEP Technical Documentation2008 Long-Term Trend (LTT) Assessment Sample Design 

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Selection of Primary Sampling Units

Public School LTT Assessment

Private School LTT Assessment

School and Student Participation Results for the LTT Assessment

Age Distribution Fractions


Unlike most of the NAEP operational assessment, the population target for the long-term trend (LTT) assessment  is defined by age rather than grade. The three age populations for the 2008 study are as follows:

  • Age 9 population: all students with birth months January 1998 through December 1998 (i.e., all students who were nine-years-old on December 31, 2007).
  • Age 13 population: all students with birth months January 1994 through December 1994 (i.e., all students who were thirteen-years-old on December 31, 2007).
  • Age 17 population: all students with birth months October 1990 through September 1991 (i.e., all students who were seventeen-years-old on September 30, 2008).

The sample was designed to be nationally representative at each of these age populations. The target population included all students in these age ranges enrolled in public and private schools. The samples were selected based on a three-stage sample design:

  • selection of primary sampling units (PSUs),
  • selection of schools within PSUs, and 
  • and selection of students within schools.

The overall sample sizes were driven by the targeted number of students for each subject. The 2008 LTT subjects were

  • reading,
  • mathematics, and
  • mathematics pilot.

The target numbers of assessments are the same for each age group (9, 13, 17) as given in the following table.

Student sample size targets for each age group (9, 13, 17), long-term trend (LTT) assessment, by subject, 2008


Public school students Private school students Total students
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2008.
Total 13,250 3,250 16,500
Reading 6,425 1,575 8,000
Mathematics 6,425 1,575 8,000
Mathematics pilot 400 100 500

These targets represent completed assessments. To get the overall sample sizes, these targets were adjusted upwards to allow for expected losses from absent, refusing, and/or ineligible schools and students (so that the completed assessment targets would be met).  The corresponding overall students sample sizes are contained in the Participation, Exclusion, and Accommodation Rates pages.

Last updated 03 February 2011 (EH)