THE NEW MEDICAL MODEL: CHRONIC DISEASE and EVIDENCE-BASED MEDICINE
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THE NEW MEDICAL MODEL: CHRONIC DISEASE and EVIDENCE-BASED MEDICINE by Jonathan Fuller A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department: Institute of Medical Science University of Toronto © Copyright by Jonathan Fuller (2016) The New Medical Model: Chronic Disease and Evidence-Based Medicine Jonathan Fuller Doctor of Philosophy Institute of Medical Science University of Toronto 2016 Abstract In the traditional medical model, physicians cure acute diseases using knowledge from the basic biomedical sciences. With the rise of chronic disease and evidence-based medicine (EBM) in the second half of the Twentieth Century, ‘the new medical model’ emerged. In the new medical model, physicians prevent or manage chronic diseases using the principles of EBM. Chronic diseases and EBM have created a host of daunting problems for modern medicine. In this thesis dissertation, my Central Aim is a philosophical analysis of chronic disease and of EBM, especially concerning treatment and prevention. I also maintain a Central Thesis: many practical problems in chronic disease care and in EBM are intimately connected to conceptual, metaphysical and epistemic problems. The practical problems include: reductionism; fractured care; multifactorialism; the growing burden of chronic diseases; treatment effect heterogeneity, treatment futility and treatment harm; cookbook medicine; the tyranny of aggregate outcomes; RCT worship; unrepresentative trials; and multimorbidity. The philosophical problems I explore are the following. In Chapter 2, I examine the nature of chronic diseases and advance a metaphysical account in which chronic diseases are bodily properties. In Chapter 3, I re-examine existing models of disease classification and argue for a new descriptive model (the ‘constitutive model’) as well as a ii new guiding principle for disease prevention (‘the monomechanism ideal’). In Chapter 4, I develop a general account of why mechanistic models often fail to predict the results of medical interventions. In Chapter 5, I reconstruct the standard model of prediction in medicine, the ‘Risk Generalization-Particularization (Risk GP) Model’. In Chapter 6, I develop a theory of causal inference in comparative group studies that illuminates the roles of randomization, confounders and causes. Finally, in Chapter 7 I show why EBM’s preferred approach to generalizing trial results, ‘simple extrapolation’, is a deeply problematic solution to the problem of extrapolation. Throughout the ongoing discussion, we indeed find that many practical problems in modern medicine are tangled up with philosophical problems. It will require both medical and philosophical wisdom to unravel them. iii For my father, a physician. iv The best physician is also a philosopher. Galen v Acknowledgments I am indebted to my thesis advisory committee: Ross Upshur, Ayelet Kuper and Paul Thompson. I was fortunate to have a PhD supervisor in Ross, who encouraged and supported me as I roamed widely both intellectually and geographically during this PhD. Ross’s profound and eclectic wisdom, as a physician and philosopher, were a source of tremendous insight and inspiration; his voluminous work on complex chronic disease care and evidence- based medicine inspired many questions explored in this dissertation. I was equally fortunate to have Ayelet as supervisor of my research fellowship in health professions education at the Wilson Centre, undertaken during this PhD. Ayelet provided endless academic and personal support. I benefited greatly from her wide-ranging expertise, and from her constant companionship at the Centre. I am also grateful for Paul’s expert guidance, especially early in the PhD when I was a fledgling graduate student studying philosophy and he gave me the tools I needed to become a philosopher. Much of this dissertation is a tribute to the work of Nancy Cartwright, who supervised me during my visit to the Philosophy Department at the University of California, San Diego in 2015. Nancy was and remains a dedicated intellectual coach and mentor whose work has shaped my thinking more than anyone else’s research. I was also privileged to have David Papineau as a supervisor during my visit to the Philosophy Department at King’s College London in 2013-14. David inexhaustibly challenged my philosophy and prompted me to think deeper. I am grateful for my close friend and collaborator Luis Flores, who shares my obsessive drive for getting to the bottom of things, and who is the coauthor of Chapter 5 of this dissertation. A version of Chapter 5 was previously published with the following citation: Fuller, Jonathan, and Luis J. Flores. 2015. "The Risk GP Model: The standard model of prediction in medicine." Studies in History and Philosophy of Biological and Biomedical Sciences 54:49-61. doi: http://dx.doi.org/10.1016/j.shpsc.2015.06.006. I am thankful to the University of Toronto’s MD-PhD Program and the Institute of Medical Science for bravely allowing me to do a philosophy of science PhD in their programs without vi much precedent to fall back on. I am also thankful for support and training at the Wilson Centre, and for the friendship of many the Centre’s fellows. I am grateful to the Philosophy Department at UCSD as well as the Philosophy Department and the Centre for the Humanities and Health at KCL for hosting me as a visiting graduate student. I graciously acknowledge funding support from the Canadian Institutes of Health Research, the W. Garfield Weston Foundation, and the McLaughlin Centre. Several people provided feedback on earlier drafts of one or more of the chapters in this dissertation, including: Ross Upshur, Ayelet Kuper, Paul Thompson, Nancy Cartwright, David Papineau, Luis Flores, Andrew Baines, Margherita Benzi, Nicholas Binney, Donald Gillies, Bennett Holman, Nicholas Howell, Maël Lemoine, Mathew Mercuri, Jeremy Simon, Benjamin Smart, Sarah Wieten, Jacob Stegenga, and anonymous journal reviewers. My work has benefited greatly from their thoughtful input, and I thank them. I am especially grateful to Jacob Stegenga, who provided an abundance of helpful feedback, deep discussion, and sincere mentorship. I am also grateful for feedback and discussion with colleagues at numerous conferences, workshops and meetings. I warmly thank my friends and colleagues in philosophy, in medicine and beyond who – one way or another – have greatly influenced me and my work. I am especially thankful to Tariq Esmail for his unfailing friendship over many years, and who first suggested to me the idea of doing a PhD in the philosophy of medicine. Lastly, I thank my family, especially my parents, for their loving support through nearly three decades. Countless conversations about healthcare with my father, a physician, continually reminded me that medicine is more than just delicious food for philosophy; medicine is about doctors muddling through as best they can in the care of patients with real health problems. It is for them that I submit this modest contribution to the philosophy of medicine. vii Contributions I am responsible for all work in this dissertation. I express my thanks to Luis Flores, who is coauthor of Chapter 5. Luis helped me to conceptualize the chapter’s research question and think through its arguments. viii Table of Contents Abstract .................................................................................................................................... ii Dedication .............................................................................................................................. iv Epigraph. ................................................................................................................................. v Acknowledgments ................................................................................................................. vi Contributions……………………..………………………………………………………..viii Table of Contents .................................................................................................................. ix List of Tables ....................................................................................................................... xiv List of Figures ....................................................................................................................... xv List of Abbreviations .......................................................................................................... xvi Chapter 1 - Introduction ........................................................................................................ 1 1.1 The Medical Model ....................................................................................................... 1 1.2 Chronic Disease ............................................................................................................. 2 1.3 Evidence-Based Medicine ............................................................................................. 4 1.4 The New Medical Model ............................................................................................... 6 1.5 Problems of Modern Medicine .................................................................................... 7 1.5.1 Reductionism ............................................................................................................ 7 1.5.2 Fractured Care ......................................................................................................... 8 1.5.3 Multifactorialism .....................................................................................................