Qualification mismatch is determined based on a comparison of a worker’s qualification level - expressed as the International Standard Classification of Education (ISCED) level corresponding to his or her highest educational qualification - and what is thought to be the required qualification level for his or her occupation code - the International Standard Classification of Occupations (ISCO) code attached to the job he or she holds. Because ISCED levels do not accurately reflect skills -not even those acquired in initial education - and ISCO codes do not accurately describe jobs, the resulting measure does not precisely describe how a worker’s skills set matches the skills needed to carry out his or her tasks at work. Skills mismatch, however, refers more precisely to a worker’s actual skills and to the skills needed in his or her specific job.