A concept taxonomy and an instrument hierarchy: tools for establishing and evaluating the conceptual framework of a patient-reported outcome (PRO) instrument as applied to product labeling claims.

OBJECTIVE: To facilitate development and evaluation of a PRO instrument conceptual framework, we propose two tools--a PRO concept taxonomy and a PRO instrument hierarchy. FDA's draft guidance on patient reported outcome (PRO) measures states that a clear description of the conceptual framework of an instrument is useful for evaluating its adequacy to support a treatment benefit claim for use in product labeling the draft guidance, however does not propose tools for establishing or evaluating a PRO instrument's conceptual framework.
METHODS: We draw from our review of PRO concepts and instruments that appear in prescription drug labeling approved in the United States from 1997 to 2007.
RESULTS: We propose taxonomy terms that define relationships between PRO concepts, including "family,""compound concept," and "singular concept." Based on the range of complexity represented by the concepts, as defined by the taxonomy, we propose nine instrument orders for PRO measurement. The nine orders range from individual event counts to multi-item, multiscale instruments.
CONCLUSION: This analysis of PRO concepts and instruments illustrates that the taxonomy and hierarchy are applicable to PRO concepts across a wide range of therapeutic areas and provide a basis for defining the instrument conceptual framework complexity. Although the utility of these tools in the drug development, review, and approval processes has not yet been demonstrated, these tools could be useful to improve communication and enhance efficiency in the instrument development and review process.