Trade union membership rate is defined as the percentage of employees who have joined a trade union. Only members under the age of 65 working in paid employment for at least twelve hours a week are taken into account.
Data in this article are based upon the Labour Survey (EBB). The results of the EBB are annual averages. No data are available for reference year 2005, as the module on trade unions was not included in the EBB in that particular year. The figures in the graphs referring to 2005 have been interpolated.