Since the 20th century, the word is being increasingly used in non-medical contexts as well, for example in corporate finance.

The most accurate form of prognosis is achieved statistically. By comparing large groups of patients by the stage of their disease, a statistical pronouncement can be made on the survival chances of a patient with a particular constellation of symptoms. Possibly the best examples are in tumor staging, where careful investigation of the degree of progression of cancer has been shown to significantly predict survival. The prognosis for well-studied chronic diseases is usually stated in terms of the percentage of patients with a similar illness who historically have survived for one, three, or five years. For example, for most prostate cancers the five year survival rate is above 90%, whereas for most lung cancers, it is less than 10%.

Unfortunately, large areas of medicine are still missing statistical figures on the exact prognosis - in these matters the doctor's previous experiences largely guides pronouncements in this matter. Medical studies have demonstrated that most doctors are overly optimistic when giving prognostic information, that is, they tend to overstate how long the patient might live. For patients who are critically ill, particularly those in an intensive care unit, there are numerical prognostic scoring systems that are more accurate. The most famous of these is the APACHE II scale. Unfortunately, this scale is most accurate in the seven days prior to a patient's predicted death.

Knowing the prognosis helps determine whether it makes more sense to attempt certain treatments or to withhold them, and thus plays an important role in end-of-life decisions.

History

For the great 19th century physicians, particularly the French school, the main aim of medicine was not to cure disease, but rather to diagnose it and achieve a satisfying prognosis of the patient's chances. Only several decades later did the focus of efforts in Western medicine shift to curing disease.