text: Some important questions remain at the end of such a report: 
  
  • The**quality of statistics and surveys fades the more irregular are the working**conditions 
  being studied. Which research methods are adequate for a clearer and more reliable evidence 
  base on these working conditions? It might require research methods different from those used 
  today, for example, more investigative case studies; it might also be helpful to evaluate the 
  **existing national working conditions surveys or statistics**under this aspect. 
  
  •**Fading employer–employee relations.**There are special research efforts necessary to study 
  the application of OSH regulations of work with weak or no employer–employee relations, for 
  example, for the self-employed and new forms of employment. 
  
  •**Surveys usually suffer a participation bias, for example, for the migrant workforce.**The 
  low participation rate of migrants can contribute to a particular underestimation regarding their 
  often unfavourable working conditions. 
  
  •**Workers in manual occupations**report**better health than administrative workers**but**less**
  **expectations to do the job until being 60 years old**. What are the reasons behind this? Is it 
  the healthy worker effect, strong occupation-related differences regarding the perception of 
  health and the expression of health problems? 502,503 