Mind the evidence gap: the use of patient-based evidence to create "complete HTA" in the twenty-first century.

The aim of this paper is to review the concept of patient-based evidence in health technology assessment (HTA), drawing on philosophical ideas of knowledge in order to judge whether current approaches to the use of evidence for HTA are complete. We draw on a number of key sources, including key papers and book chapters, discussion forums, agency reports, and conference presentations. We develop the potential dimensions of patient-based evidence, describe its key attributes, and consider its future development. Patient-based evidence has the potential to be a key concept in HTA, comprised of a series of related elements of importance to patients. We recognize that we raise more questions than can be answered, but as an emerging concept, recognition and understanding of patient-based evidence is still developing. The concepts and methods that support its application in HTA require urgent development. We conclude that clinical and economic forms of evidence are not enough for HTA. For HTA to be complete, we need to consider all relevant aspects of the phenomena, including patient-based evidence. There is now an urgent need for the global research and HTA community to work together to realize the full potential of patient-based evidence through conceptual and methodological development and wider recognition. We advocate that a task force be set up to address these urgent issues.