In addition, the project will consider pathophysiological timing. This is of particular importance in sepsis where current biological models suggest that there is a phased response to infection.{Riedemann:2003p82} In this case, it is possible that patients are admitted to critical care at different phases of disease; moreover, these phases may be clinically relevant and affect response to treatment. pathophysiological delay will be estimated using the concept of illness trajectories (which also may have a biological correlate){Osuchowski:2006p2107}. This means that a patient who is slowly deteriorating is likely to have been ill for longer. In other words, their pathophysiological time zero will be earlier than another patient who is is rapidly deteriorating. This illness trajectory will be estimated by measuring the change in severity of illness between ward assessment and ICU admission. The effect of these illness trajectories, and therefore of the pathophysiological timing of ICU admission, will be evaluated with particular attention to severe sepsis.