In addition, the implementation of semiparametric matching methods allows us to compare more comparable samples and, thus, control for additional sources of bias related to common support issues in the data.
Even though the existing research is far too limited for any definite conclusions, we may construct the hypothesis that grade-based sampling strategies result in more comparable samples when we compare student achievement across countries.
Comparable tests mean that we have to use a common metric when we compare the results from different studies, and comparable samples mean that the samples should not differ if we compare them over time or across countries.
Regardless of the respective approach, it is crucial to note that any sampling approach results in certain differences that violate the assumption of having comparable samples.
The decision to conduct cross-national comparative studies on the yield of educational systems by testing the achievements of comparable samples of students was reached in the late 1950s at the UNESCO Institute of Education in Hamburg, Germany.
Similar surveys were done with comparable samples of women in 1982, 1995 and 2002, and some findings "are quite persistent" over the decades, said an author of the report, William D. Mosher, a statistician with the center.
