The QALY at 50: One story many voices.

Research on quality adjusted life year (QALY) has been underway for just over 50 years, which seems like a suitable milestone to review its history. The purpose of this study is to provide a historical overview of why the QALY was developed, the key theoretical work undertaken by Torrance, Bush and Fanshel and how two seminal papers shaped its subsequent development. Moving the QALY forward - there are several historical and reflective exercises. The historical interplay between politics, policy and the challenges facing the National Health Service (NHS) in formulating the QALY concept in the UK has been explored in some depth already, whilst the conceptualization and development of the methodological framework is relatively underexplored. We address this gap by viewing the QALY through the lens of the methodological debates, reflecting upon two key papers underpinning the QALY methodology and how these methods have been developed over time. In part the changes in technology e.g. Google Scholar, and the availability of tools to search for early uses of the QALY allow us to better understand the historical context in which the theoretical development of the QALY has taken place. Here we celebrate two seminal papers that shaped early QALY development. The first section provides a history of these papers, summaries their contributions and explores the uptake of these papers over time. The second section reviews the methodological debates that have surrounded the QALY over the last 50 years and looks at how the QALY has moved to address these challenges. The third section presents the voices of diverse commentators representing the field of health economics who have contributed to the subsequent development of the QALY in both theoretical and empirical capacities and captures their thoughts about future research and policy use of QALYS.