A number of factors can limit the comparability of statistics on employment by level of educational attainment between countries or over time. Comparability of employment statistics across countries is affected most significantly by variations in the definitions used for the employment figures. Differences result from age coverage, such as the lower and upper bounds for labour force activity. Estimates of employment are also likely to vary according to whether members of the armed forces are included. Another area with scope for measurement differences has to do with the national treatment of particular groups of workers. The international definition of employment calls for inclusion of all persons who worked for at least one hour during the reference period.
Workers could be in paid employment or in self-employment, including in less obvious forms of work, some of which are dealt with in detail in the resolution adopted by the 19th ICLS, such as unpaid family work, apprenticeship or non-market production. Some countries measure persons employed in paid employment only and some countries measure “all persons engaged”, meaning paid employees plus working proprietors who receive some remuneration based on corporate shares. Other possible variations to the norms pertaining to measurement of total employment include hours limits (beyond one hour) placed on contributing family members before for inclusion in employment.
Comparisons can also be problematic when the frequency of data collection varies widely. The range of information collection can run from one month to 12 months in a year. Given the fact that seasonality of various kinds is undoubtedly present in all countries, employment figures can vary for this reason.
The way in which employed individuals are assigned to educational levels can also severely inhibit cross-country comparisons. Many countries have difficulty establishing links between their national educational classification and ISCED, especially with respect to technical or professional training programmes, short-term programmes and adult-oriented programmes (ranging around levels 3, 4 and 5 of ISCED-97 and ISCED-11). In numerous situations, ISCED classifications are not strictly adhered to; a country may choose to group together some ISCED categories. It is necessary to pay close attention to the notes in order to ascertain the actual distribution of education levels before making comparisons.
An issue that affects several countries in the European Union originates from the way in which those who have received their highest level of education in apprenticeship systems are classified. The classification of apprenticeship in the “secondary” level – despite the fact that this involves one or more years of study and training beyond the conventional length of secondary schooling in other countries – can lower the reported proportion of the labour force or population with tertiary education, compared with countries where the vocational training is organized differently. This classification issue substantially reduces the levels of tertiary education reported by Austria and Germany, for instance, where the participation of young people in the apprenticeship system is widespread.
There is also the potential for further confusion as to how a person’s educational level is to be defined. Ideally, when making cross-country comparisons, all data should refer to the highest level of education completed, rather than the level in which the person is currently enrolled, or the level begun, but not successfully completed. However, because data are usually derived from household surveys, the actual definition used will inevitably depend on each respondent’s own interpretation.