Prognosis is a medical term to describe the likely outcome of an illness. When applied to large populations, prognostic estimates can be very accurate: for example the statement "45% of patients with severe septic shock will die within 28 days" can be made with some confidence, because previous research found that this proportion of patients died. However, it is much more difficult to translate this into a prognosis for an individual patient: additional information is needed to determine whether a patient belongs to the 45% who will succumb, or to the 55% who survive.[1]