NAEP is an ongoing, congressionally mandated survey designed to
measure what students know and can do. The goal of NAEP is to
estimate educational achievement and changes in that achievement
over time for American students of specified grades as well as
for subpopulations defined by demographic characteristics and
by specific background characteristics and experiences. In 1996,
NAEP collected mathematics and science data from nationally representative
samples of students in public and private schools in grades 4,
8, and 12. Additionally, directly comparable state assessments
were conducted in public and private schools in participating
states and jurisdictions at grade 4 for mathematics and at grade
8 for mathematics and science. For many of the states and jurisdictions
the sample of private school students was not adequate to support
reporting of private school results. Accordingly, state-level
results were reported by NAEP for the public schools samples only.
State-level NAEP mathematics and science results are available
for grade 8 public school students in 44 states and jurisdictions.

TIMSS is the largest and most ambitious study ever conducted by
the International Association for the Evaluation of Educational
Achievement (IEA). TIMSS is an international comparative study
designed to provide information about educational achievement
and learning contexts for the participating countries. Each participating
country assessed mathematics and science in the two grades with
the largest proportion of 13-year-olds (grades 7 and 8 in most
countries, including the United States). Mathematics and science
results are available for 41 countries for the higher of these
grade levels—which, for convenience, will be referred to as the
grade 8 level in this report.

The U.S. results are based on a sample of students from public
and private schools. In addition, three states opted to collect
grade 8 TIMSS data from representative samples of their students.
Minnesota participated in a state-level administration of grade
8 TIMSS mathematics and science in 1995, while Missouri and Oregon
participated in state-level administrations of grade 8 TIMSS in
1997. All three states also participated in the 1996 State NAEP.
Thus, released public school NAEP results are available for all
three states, as well as released TIMSS results for Minnesota.
However, the TIMSS results for Missouri and Oregon cannot be explicitly
included in this report since those results have not yet been
publicly released.

A number of key characteristics of the NAEP and TIMSS results
have a bearing on the adequacy of any link between the two assessments.
These include the following:

- Both NAEP and TIMSS are based on complex probability samples of
the student population. Both U.S. samples include public and private
students in grade 8. The sample sizes for the two assessments
in the United States are similar, being 7,146 and 7,087 for NAEP
and TIMSS grade 8 mathematics, and 7,774 and 7,087 for NAEP and
TIMSS grade 8 science.
- TIMSS was conducted in the United States (and in most Northern
Hemisphere countries) in April and May 1995. NAEP was conducted
January through March 1996. Thus, the TIMSS results are applicable
to the achievement of the 1995 student population at the end of
the school year, while the NAEP results are applicable to the
achievement of the 1996 student population some months before
the end of the school year.
- The frameworks that defined the NAEP and TIMSS assessments are
not identical but appear similar. Both assessments include multiple-choice
and short- and extended-constructed response questions, but NAEP
has a higher proportion of constructed response items than does
TIMSS. The two assessments have no items in common. (Appendix
A contains the results of a content analysis of the NAEP and TIMSS
assessments.)
- In TIMSS, the same students participated in both the mathematics
and science testing, with 90 minutes total testing time across
the two subjects or 45 minutes for each. Both mathematics and
science were mixed within each booklet. In NAEP, each sampled
student received either a mathematics or a science instrument.
Total testing time for the mathematics instrument was 45 minutes,
comparable to TIMSS mathematics. Total testing time for NAEP science
was 90 minutes at grade 8, including 30 minutes of hands-on tasks.
- Both NAEP and TIMSS scaled their data using Item Response Theory
(IRT) techniques. TIMSS used a Rasch partial credit model to create
a single scale for each subject, while NAEP used a variety of
scaling models (two and three parameter logistic and generalized
partial credit) to develop subscales for mathematics and science.
NAEP mathematics and science composites were then created as weighted
averages of the mathematics and science subscales. Both NAEP and
TIMSS used methodology to account for the imprecision of measurement
of individual students' abilities (plausible values). These allow
for appropriate estimates for any subgroups contained in the conditioning
model. However, grade 8 TIMSS only conditioned for grade within
country, while NAEP conditioned on several hundred variables.

Clearly, while similar, the NAEP and TIMSS assessments do differ
in ways that will impact the link between the two. The next section
reviews the types of linking available and indicates what the
NAEP-TIMSS link will be.