Objective: To present an explanatory framework for understanding prognosis and illustrate it using data from a systematic review.
Study design and setting: A framework including three phases of explanatory prognosis investigation was adapted from earlier work and a discussion of causal understanding was integrated. For illustration, prognosis studies were identified from electronic and supplemental searches of literature between 1966 and December 2006. We extracted characteristics of the populations, exposures, and outcomes and identified three phases of explanatory prognosis investigation: Phase 1, identifying associations; Phase 2, testing independent associations; and Phase 3, understanding prognostic pathways. The purpose of each phase is exploration, confirmation, and development of understanding, respectively.
Results: It is important to consider a framework of explanatory prognosis studies for: (1) defining the study objectives, (2) presenting the study methods and data, and (3) interpreting and applying the results of the study.
Conclusion: When conducting and reporting prognosis studies, researchers should consider the approach to prognosis (explanatory or outcome prediction) and phase of investigation, use best methods to limit biases, report completely, and cautiously interpret results. Readers of health care research will then be better able to evaluate the goals and interpret and appropriately use the results of prognosis studies.