Blanchard and Wolfers studied 8 market rigidities in 20 countries (including the EU, USA, Canada, and Japan) between the years 1960-96. The unemployment rate in an imaginary composite of all the studied countries should have risen by 7.2% in this period. But unemployment increased by twice as much in countries with strict employment protection laws compared to countries with laxer labour legislation.
Unemployment in the country with the most generous unemployment benefits grew five times more than in the most parsimonious one. It grew our times faster in countries with centralized wage bargaining than in countries with utterly decentralized bargaining. Labour market rigidities all amplify the effects of asymmetrical shocks - which bodes ill for the eurozone.
Other studies (e.g., the 1994 OECD one year study, the more substantial DiTella-MacCullouch study) seem to support these findings. The transition from a rigid to a flexible labour market does not yield immediate results because it increases labour force participation. But the unemployment rate is favorably affected later.