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NAEP Assessment Sample Design → NAEP 2012 Sample Design → 2012 Long-Term Trend (LTT) Assessment Sample Design

NAEP Technical Documentation2012 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 2012 study are as follows:

  • age 9 population: all students with birth months January 2002 through December 2002 (i.e., all students who were nine-years-old on December 31, 2011)
  • age 13 population: all students with birth months January 1998 through December 1998 (i.e., all students who were thirteen-years-old on December 31, 2011).
  • age 17 population: all students with birth months October 1994 through September 1995 (i.e., all students who were seventeen-years-old on September 30, 2012)

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 as follows:

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

The overall sample sizes were driven by the targeted number of students for each subject. The 2012 LTT subjects were as follows:

  • mathematics
  • reading
  • mathematics pilot
  • reading pilot

The pilot assessments were integrated with the operational assessments with some students taking one pilot and one operational block.

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 and school type, 2012


Public school students Private school students Total students
NOTE: O = Operational assessment only; O/P = Integrated Operational and Pilot assessment.  Detail may not sum to totals because of rounding.
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2012 Long-Term Trend Assessments.
Total 15,300 1,700 17,000
Mathematics (O) 5,900 650 6,500
Reading (O) 5,900 650 6,500
Mathematics (O/P) 1,800 200 2,000
Reading (O/P) 1,800 200 2,000

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 05 June 2013 (JL)