The most recent addition to the family of international comparative large-scale studies of education is OECDs “Programme for the International Assessment of Adult Competencies” (PIAAC), which focuses on literacy, numeracy and problem-solving skills in representative samples of persons 16 to 65 years old. So far data is available for 24 countries. The results demonstrate striking performance differences between different age groups, with increasing levels of performance from age 16 to around age 25 and successively declining levels of performance thereafter. This general pattern is consistent across countries, but there also are country differences in the size of the age-group differences.

In a cross-sectional study, the observed differences in level of performance between age groups are the result of a combination of age effects and cohort effects. Age effects are due to individual factors such as maturation and decay, while cohort effects are due to circumstances and events that are unique to an age cohort, such as quantity and quality of education, nutrition and health care, and demographic factors, just to mention a few. This suggests that the PIAAC data could be a source of information about differences in the quality of schooling received by different age-cohorts within countries and across countries, given that the influence of age-effects and other cohort effects can be controlled for. One possible approach to control for age-effects is to compare the levels of performance for the age-groups of a particular country with the mean level of performance for corresponding age groups of all the other countries.

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