“… The union employment literature employs various measures of union strength, depending on the institutional setting in the country and the data sets available. The most common measures are union density (the share of union members among all employees) (Blanchflower et al ., , Machin and Wadhwani, , Bronars et al ., , Dunne and MacPherson, , Addison et al ., , Wooden and Hawke, , Krol and Svorny, , Bryson and Dale‐Olsen, ) or union recognition for collective bargaining (Blanchflower et al ., , Machin and Wadhwani, , Leonard, , Blanchflower and Burgess, , Booth and McCulloch, , Addison and Belfield, , Bryson, , Bryson and Dale‐Olsen, , Bryson and Nurmi, ), while other authors use variations of these measures. …”