Reference-Class Problems Are Real: Health-Adjusted Reference Classes and Low Bone Mineral Density.

Elselijn Kingma argues that Christopher Boorse's biostatistical theory (the BST) does not show how the reference classes it uses are objective and naturalistic. Recently, philosophers of medicine have attempted to rebut Kingma's concerns. I argue that these rebuttals are theoretically unconvincing, and that there are clear examples of physicians adjusting their reference classes according to their prior knowledge of health and disease. I focus on the use of age-adjusted reference classes to diagnose low bone mineral density in children. In addition to using the BST's age, sex, and species, physicians also choose to use other factors to define reference classes, such as pubertal status, bone age, body size, and muscle mass. I show that physicians calibrate the reference classes they use according to their prior knowledge of health and disease. Reference classes are also chosen for pragmatic reasons, such as to predict fragility fractures.

Osteoporosis and risk of fracture: reference class problems are real.

Elselijn Kingma argues that Christopher Boorse's biostatistical theory does not show how the reference classes it uses-namely, age groups of a sex of a species-are objective and naturalistic. Boorse has replied that this objection is of no concern, because there are no examples of clinicians' choosing to use reference classes other than the ones he suggests. Boorse argues that clinicians use the reference classes they do because these reflect the natural classes of organisms to which their patients belong. Drawing on a thorough exploration of how the disease osteoporosis is defined in adults, I argue that clinicians do indeed make choices about which reference classes to use in diagnosis. Clinicians use young adult reference classes to diagnose osteoporosis in elderly patients. They also use young female reference classes to diagnose osteoporosis in elderly males. Clinicians adjust their reference classes so that the diagnosis of osteoporosis reflects a person's risk of sustaining a fragility fracture. The ethical intuition that people with the same risk of fracture should receive the same diagnosis overwhelms the naturalistic intuition that reference classes should reflect natural classes of organisms of uniform functional design. Clinicians construct a variety of reference class types, including pathological reference classes and epidemiological population-specific reference classes, to serve this ethical intuition. I show how clinicians use several reference classes at once so that they can more accurately predict risk of fracture. Ultimately, the reference classes chosen and used in medical practice are quite different from those proposed in naturalistic philosophy of medicine.

On the Origin of Sensitivity and Specificity.

Although it is commonly said that the notions of sensitivity and specificity were first defined by Jacob Yerushalmy in 1947, the sensitivity and specificity of diagnostic tests have been assessed as far back as the early 1900s. These notions share a common origin with the development of serology. They were originally immunologic concepts, closely associated with the development of complement fixation reactions for syphilis. Here, the authors trace how immunologic sensitivity and specificity were transformed into diagnostic sensitivity and specificity. By relocating the origins of these concepts to the early 20th century, they highlight how these origins were bound to then-commonplace assumptions about specific infectious disease entities.

The function of the heart is historically contingent.

Some philosophers of medicine argue that there are objective facts about the biological function of organs, and that these facts are used to objectively define diseases. The function of the heart is taken to be particularly obvious and well established. Contrary to this, I argue that the function of the heart is not fixed by nature, but rather that it is historically contingent. The disease heart failure results from the dysfunction of the heart. In opposition to the common-sense intuitions of philosophers, medics do not define heart failure simply as a reduced cardiac output, and up to half of patients with heart failure have a normal cardiac output. The present day medical definition of heart failure is thus counter-intuitive. In the early twentieth century, however, medics did define heart failure as a reduced cardiac output. This view was opposed in the 1930s, when a similar definition of heart failure to the one used today was put forward. I look closely at this historical episode, in order to explore the reasons for this development. I use this history to argue that present day knowledge of heart failure is not the inevitable result of careful observation of patients, but rather is historically contingent.

The function of the heart is not obvious.

It is widely believed that the function of the heart is obviously to pump blood. I argue here that it is not. The definition, presentation, and pathophysiological explanation of heart failure, as well as the measurement of cardiac dysfunction, are not as might be expected if the function of the heart was simply to pump blood. Far from being obvious, many central features of heart failure are still being investigated. This has important implications for philosophical debates about health and disease. According to naturalists like Christopher Boorse, medical practice is founded on a well-established body of physiological knowledge, which provides the one true account of the biological function of organs. On this naturalistic view, there should only be one account of the pathophysiology of heart failure in use in medical practice. This account of the pathophysiology of heart failure should be well-established, as opposed to uncertain. Medics should use this physiological knowledge to inform their clinical practice, and not vice versa. Clinical considerations, such as whether patients respond to therapy, should not inform debates about what the pathophysiology of heart failure is. I will show this is not the case. The handling of knowledge of the biological function of the heart in medical practice differs substantially from Boorse's account.

Nosology, ontology and promiscuous realism.

Medics may consider worrying about their metaphysics and ontology to be a waste of time. I will argue here that this is not the case. Promiscuous realism is a metaphysical position which holds that multiple, equally valid, classification schemes should be applied to objects (such as patients) to capture different aspects of their complex and heterogeneous nature. As medics at the bedside may need to capture different aspects of their patients' problems, they may need to use multiple classification schemes (multiple nosologies), and thus consider adopting a different metaphysics to the one commonly in use.