The association between adverse events and nursing care: measurement problems. Staffing of RNs below target levels has been associated with increased adverse events, included mortality. Some events may be directly associated to lack of surveillance or care, others occur as a result of neglected care and cannot be associated to the shift with levels of nurses below the target. However, a close look to negative events, neglecting positive events provides an incomplete view. Such studies have been criticized because they have not shown a direct link between the level of staffing and individual patient experiences, often did not control for sill mix and did not explore in depth what nurses do and what are their priorities when there is an higher workload. Often these studies present data with mean values ignoring that nurse staffing is not the same across an entire hospital and nursing care is delivered in geographically-based units, with wide variation in staffing levels. A future challenge of research is to combine a descriptive-quantitative approach with the collection of more qualitative data and prospective designs.