For all persons employed aged 15 and older, occupation was recorded by country of birth. Occupations are defined on the basis of the International Standard Classification of Occupations (ISCO) at the three‐digit level. At the two‐digit level,
the data are crossclassified by education levels and gender. Data are available for the 28 countries covered by the publication, although they are only available the at the one‐digit level for Italy. For Japan, Turkey and the United States, national classifications
cannot be matched to ISCO even at aggregate level. For the purposes of this publication, the occupations have been regrouped into three categories corresponding to three different levels of qualification: professionals (ISCO major groups 1 and 2), technicians
(ISCO major groups 3 and 4) and operators and labourers (all other groups).