It is, however, not informative about the educational opportunities available to today’s youth. It may therefore be complemented by a measure of educational expectancy, which can be defined as the number of years of schooling that youth aged 15 today may expect to undertake while aged 15 to 29, based on the current enrolment of people aged 15-29. The threshold has been set at 15, the compulsory school age in many OECD countries, as the challenge is to extend education beyond that.