Why have unions declined over the last 30 years?

Account for the collapse of private sector trade unions in industrialised economies since the 1980s. Why has the experience of public sectors been different?

In the 1980s 54.5% of employees were trade union members but by 2000 this number was below 30%. This decline in unions can be seen through a variety of measures; in 1980 64% of all workplaces recognised at least one union, this dropped to 42% by 1998; in 1984 some 70% of employees were with a workplace which conducted some form of collective bargaining, by 2004 this figure was at 39%. Many factors have been proposed for this decline of trade unions in the private sector and to a limited extent in the public sector. [...]