text: There surely is also a bias of responses regarding**socially not-at-all or not-well-accepted**topics like 
  undeclared work or personal behaviour, for example, taking cognitive or performance-enhancing drugs 
  at work. 
  
  Some structural factors make an unambiguous and accurate assessment of the state of OSH in the EU 
  particularly difficult: 
  
  the**variety**of OSH systems and infrastructures in EU Member States and its impact on 
  (harmonised) EU-wide data collection and research approaches; 
  the**issues**related to the use (or even new development) of**reliable and measurable**
  **indicators**, the methodological differences between different survey and research 
  approaches; 
  the assessment of the**effectiveness of preventive actions and the evaluation of the**
  **quality and quantity of outcomes, injuries and diseases**; and 
  the**continuous development**and**structural changes**of working conditions and the social, 
  economic and technological context of OSH. 
  
  **1)**
  
  **2)**
  
  **4)**