Duration is measured as the duration of joblessness. Duration of "Less than one month" refers to the duration of unemployment during the previous four weeks, including the survey reference week.

Up to year 2005 it was not possible to disaggregate UN1 (duration of unemployment of less than one month) and as a result this category was included in UN2 (>1 month and less than 3 months). As of 2005, the distinction is possible and UN1 is now a separate category. Up to 2005, the survey did not ask the duration of unemployment for "people who have already found a job which will start later".  These persons are classified in UNK (unknowns).  From 2005, this question is posed for these people.