Users' Guides to the Medical Literature
Evidence-Based Medicine Working Group

Are the Results Valid?
Was a defined representative sample of patients assembled at a similar point in the course of disease?
Was follow-up sufficiently long and complete?
Were objective and unbiased outcome criteria used?
Was there adjustment for important prognostic factors?

What Are the Results?
How likely are the outcomes over time?
How precise are the estimates of prognosis?

Will the Results Help Me in My Patient Care?
Were the study patients similar to my own ?
Will the results lead directly to selecting therapy?
Are the results useful for counseling patients?

JAMA 1994; 272: 234 - 237

Prognosis of a disease refers to its possible outcomes and the likelihood that each one will occur.

Prognostic Results are the number of events that occur over time, expressed in:
a. absolute terms: e.g. 5 year survival rate.
b. relative terms: e.g. risk from prognostic facto
c. survival curves: cumulative events over time

A Prognostic Factor is a patient characteristic the can predict that patient's eventual outcome:
a. demographic: e.g. age, sex, race
b. disease-specific: e.g. tumor stage
c. co-morbid: other co-existing conditions

Articles that report prognostic factors often use two independent patient samples:
The Derivation Set asks, "What factors might predict patient outcome
The Validation Set asks, "Do these prognostic factors predict patient outcomes accurately?"

Finding An Article on Prognosis
Explode Cohort Studies
Prognosis (tw)

[see ACP J Club 1995 July-Aug; A12 - A14]