TIMSS COVERAGE INDEX FOR FINAL-YEAR ASSESSMENT
http://timss.bc.edu/timss1995i/TIMSSPDF/SRAppA.pdf
A further difficulty in defining the desired population for the final-year
assessment is that many students drop out before the final year of any track.
Thus a TIMSS Coverage Index (TCI) was calculated that quantifies the
proportion of the entire school-leaving age cohort that is covered by the
TIMSS final-year sample in each country. The TCI was defined as follows:
TCI = Total Enrollment in TIMSS Grades 1995/(Total National Population Aged 15 -19 in 1995)
The
numerator in this expression is the total enrollment in the grades tested byTIMSS, estimated from the weighted sample data. This estimate corresponds to
the size of the population to which the TIMSS results generalize and makes
appropriate provision for student non-response. It does not include students
who are no longer attending school or students who were excluded from the
sample on grounds of physical or other disability. It also does not include
students who were repeating the final grade. Because some students repeat
the final year of a track, or take the final year in more than one track at
different times, they may be in the final year of a track without completing
their secondary education that year. On the one hand, students who are not
completing their education still have the potential to gain further knowledge
in additional years of schooling, and thus will not have attained their full yield
at the time of the TIMSS assessment. On the other hand, and of more serious
concern, the presence both of students who are repeating the final track and
of those who will repeat that track can contribute a substantial downward bias
to the estimated achievement of the population. Repeating students would be
represented twice in the population, and are likely to be lower-achieving on
average than those who do not repeat. The only practical way for TIMSS to
deal with this problem was to exclude students who were repeating the final
year. Thus, the population of final-year students is formally defined as those
students taking the final year of one track of the secondary system for the first
time.
The
denominator in the expression is an estimate of the school-leaving agecohort size. Since the age at which students in upper-secondary school may
leave school varies, TIMSS estimated the size of the school-leaving age cohort
by taking the average of the size of the 1995 age cohorts for 15-, 16-, 17-, 18-,
and 19-year-olds in each country. (Although the estimate was generally based
on the 15-19 age group, there were exceptions; for example, in Germany it
was based on the 17-19 age group.) This information was provided by NRCs
from official population census figures in their countries. This approach
reflects the fact that students in the final year of secondary school are likely to
be almost entirely a subset of the population of 15- to 19-year-olds in most
countries. Table A.4 presents the computation of the TCI for each country.