Table 1.

Levels of Evidence for Prognostic Factor Studies

Study Phase	Description
Phase I Exploratory	Associations between potential prognostic factors and health outcomes explored in a descriptive way. Only crude (univariable) associations are reported.
Phase II Exploratory	Includes use of well-formulated comparison groups, stratified analyses, or multivariable analyses to identify sets of predictors.
Phase III Confirmatory	The goal is to test a specific hypothesis to confirm or disconfirm an independent relationship between an identified prognostic factor and a health outcome, while explicitly identifying and controlling for confounding.