Counting how much and determining under what circumstances diseases occur are the basic principles upon which preventive health programmes are built. The lack of accurate surveillance information leads to the inability to allocate appropriate resources, the inability to initiate and prioritise targeted interventions, and the inability to evaluate the effectiveness of those interventions. The paper by Friedman and Forst¹ in this issue (see page 454) highlights the complexity of answering on what first appear to be relatively simple questions: (1) how many occupational injuries and illnesses occur each year? and (2) are the rates of occupational injuries and illnesses changing over time? The problem they address is how the rules and definitions of recording what is an occupational injury or illness may change the quantitative measures of those conditions. Although the data they examine are specific to the US, the issue they address is of concern for surveillance systems in all countries.

Theoretically, surveillance of work-related injuries and illnesses has a potential advantage over reporting systems for non-work-related conditions, because the employer could be an additional reporting source that complements …