The data usually refer to the first quarter of the calendar year, or the average of the first three months, thereby excluding summer employment. The indicator relies on the distribution of 15-29 year-olds in education, work or neither of the two. It is thus a good proxy of the numbers of years that an individual is likely to spend in education between age 15 and 29. However, this indicator may not reflect drop-out rates and temporary interruptions of study. Another limitation is that long study durations (i.e. beyond the prescribed time) will result in an overestimate of this indicator.