The "natural history" of health technology assessment.

The collective experience of health technology assessment (HTA) in different countries delineates a pattern of development, a "natural history," of HTA in three phases: emergence, consolidation, and expansion. This study examines the rationale for HTA, definitions of its scope and breadth, its methods and organizational models, and its knowledge translation strategies, as HTA moves from one phase to the next. The study then identifies factors that facilitate or delay the transitions.