Ideal (optimal) number of pupil-years required (i.e. in the absence of repetition and dropout) to produce a number of graduates from a given school-cohort for a cycle or level of education expressed as a percentage of the actual number of pupil-years spent to produce the same number of graduates. Input-output ratio, which is the reciprocal of the coefficient of efficiency, is often used as an alternative. N.B. One school year spent in a grade by a pupil is counted as one pupil-year.

Divide the ideal number of pupil-years required to produce a number of graduates from a given school-cohort for the specified level of education, by the actual number of pupil-years spent to produce the same number of graduates, and multiply the result by 100. The coefficient of efficiency is calculated on the basis of the reconstructed cohort method, which uses data on enrolment and repeaters for two consecutive years.

Number of graduates and dropouts by length of study. These data can also be derived by using the reconstructed cohort model, which requires enrolment by grade for two consecutive years (years t and t+1); number of repeaters by grade for year t+1 and number of graduates for year t.

School register, school survey or census for data on repeaters and enrolment.

Results approaching 100% indicate a high overall level of internal efficiency in producing graduates and no wastage due to repetition and dropout. Coefficients below 100% reflect the impact of repetition and dropout on the efficiency of the educational process in producing graduates. As the reciprocal, the optimum input-output ratio is one, and inefficiency arises from any point which is greater than one.

Given that this indicator is usually derived using cohort analysis models that are based on a number of assumptions, and owing to the highly synthetic nature of this indicator, care should be taken in the use of the results in comparing education systems. From a conceptual viewpoint, having most pupils (or students) graduating within the prescribed duration of the cycle is optimal with regard to economic efficiency and resource utilization, but this does not necessarily imply achievement of the expected learning outcomes. Also, according to this calculation method, early dropouts (i.e. from lower grades) can result in higher internal efficiency than late dropout (i.e. from higher grades); this means that efficiency from the economic point of view can be in contradiction with educational objectives aiming at retaining pupils in schools until higher grades when they would have acquired the desired knowledge and skills.

This is a synthetic indicator of the internal efficiency of an educational system. It summarises the consequences of repetition and dropout on the efficiency of the educational process in producing graduates.

Since the calculation of this indicator is based on pupil-flow rates, its reliability depends on the consistency of data on enrolment and repeaters in term of coverage over time and across grades. Differences in national regulations concerning the number of repetitions allowed constitute an aspect to be taken into account when using this indicator for cross-country comparisons.

By sex and by school type (private/public).