John Worrall

What Evidence in Evidence‐Based Medicine?

Evidence‐Based Medicine is a relatively new movement that seeks to put clinical medicine on a firmer scientific footing. I take it as uncontroversial that medical practice should be based on best evidence—the interesting questions concern the details. This paper tries to move towards a coherent and unified account of best evidence in medicine, by exploring in particular the EBM position on RCTs (randomized controlled trials).

Why There's No Cause to Randomize

The evidence from randomized controlled trials (RCTs) is widely regarded as supplying the ‘gold standard’ in medicine—we may sometimes have to settle for other forms of evidence, but this is always epistemically second-best. But how well justified is the epistemic claim about the superiority of RCTs? This paper adds to my earlier (predominantly negative) analyses of the claims produced in favour of the idea that randomization plays a uniquely privileged epistemic role, by closely inspecting three related arguments from leading contributors to the burgeoning field of probabilistic causality—Papineau, Cartwright and Pearl. It concludes that none of these further arguments supplies any practical reason for thinking of randomization as having unique epistemic power. 1. Introduction2. Why the issue is of great practical importance—the ECMO case3. Papineau on the ‘virtues of randomization’4. Cartwright on causality and the ‘ideal’ randomized experiment5. Pearl on randomization, nets and causes6. Conclusion Introduction Why the issue is of great practical importance—the ECMO case Papineau on the ‘virtues of randomization’ Cartwright on causality and the ‘ideal’ randomized experiment Pearl on randomization, nets and causes Conclusion

Prediction and the periodic table

Abstract The debate about the relative epistemic weights carried in favour of a theory by predictions of new phenomena as opposed to accommodations of already known phenomena has a long history. We readdress the issue through a detailed re-examination of a particular historical case that has often been discussed in connection with it—that of Mendeleev and the prediction by his periodic law of the three ‘new’ elements, gallium, scandium and germanium. We find little support for the standard story that these predictive successes were outstandingly important in the success of Mendeleevs scheme. Accommodations played an equal role—notably that of argon, the first of the ‘noble gases’ to be discovered; and the methodological situation in this chemical example turns out to be in interesting ways different from that in other cases—invariably from physics—that have been discussed in this connection. The historical episode when accurately analysed provides support for a different account of the relative weight of prediction and accommodation—one that is further articulated here.

Scientific Discovery and Theory-Confirmation

Although I find most recent challenges to older ‘positivistic’ views in philosophy of science either unchallenging or unconvincing, there is one respect in which the new ‘post-positivists’ are, I believe, definitely right and the older ‘positivists’ definitely wrong. Reichenbach, Carnap, Popper and others all agreed that philosophy of science is exclusively concerned with the logical analysis of the merits of theories already ‘on the table’. Of course, these thinkers were ready to allow that the question of how a theory arrived on the table could be a fascinating one, but they held that it was a question of no interest to a philosopher as such. In particular, to hold that the origins of a theory have any relevance for the appraisal of its scientific merits was, according to these philosophers, to commit one form of the ‘genetic fallacy’.

The Ways in which the Methodology of Scientific Research Programmes Improves on Popper’s Methodology

A theory is scientific rather than pseudoscientific if it is capable of receiving genuine ‘support’ from the ‘facts’. One scientific theory is better than another rival theory if it is better supported by the facts than its rivals. Although some would reject the term ‘support’ and replace it by ‘confirm’ or ‘corroborate’, most recent attempts to provide an objective and generally applicable criterion of scientific merit have started essentially from these two assumptions. But when does a fact provide genuine support for a theory? And when do the facts support one theory better than another?

Evidence and Ethics in Medicine

Ethics and epistemology in medicine are more closely and more interestingly intertwined than is usually recognized. To explore this relationship, I present a case study, clinical trials of extracorporeal membrane oxygenation (ECMO; an intervention for persistent pulmonary hypertension of the newborn).Three separate ethical issues that arise from this case study—whether or not it is ethical to perform a certain trial at all, whether stopping rules for trials are ethically mandated, and the issue of informed consent—are all shown to be intimately related to epistemological judgments about the weight of evidence. Although ethical issues cannot, of course, be resolved by consideration of epistemological findings, I argue that no informed view of the ethical issues that are raised can be adopted without first taking an informed view of the evidential-epistemological ones.

Miracles and Models: Why reports of the death of Structural Realism may be exaggerated

What is it reasonable to believe about our most successful scientific theories such as the general theory of relativity or quantum mechanics? That they are true, or at any rate approximately true? Or only that they successfully ‘save the phenomena’, by being ‘empirically adequate’? In earlier work I explored the attractions of a view called Structural Scientific Realism (hereafter: SSR). This holds that it is reasonable to believe that our successful theories are (approximately) structurally correct (and also that this is the strongest epistemic claim about them that it is reasonable to make). In the first part of this paper I shall explain in some detail what this thesis means and outline the reasons why it seems attractive. The second section outlines a number of criticisms that have none the less been brought against SSR in the recent (and as we shall see, in some cases, not so recent) literature; and the third and final section argues that, despite the fact that these criticisms might seem initially deeply troubling (or worse), the position remains viable.

Underdetermination, realism and empirical equivalence

Are theories ‘underdetermined by the evidence’ in any way that should worry the scientific realist? I argue that no convincing reason has been given for thinking so. A crucial distinction is drawn between data equivalence and empirical equivalence. Duhem showed that it is always possible to produce a data equivalent rival to any accepted scientific theory. But there is no reason to regard such a rival as equally well empirically supported and hence no threat to realism. Two theories are empirically equivalent if they share all consequences expressed in purely observational vocabulary. This is a much stronger requirement than has hitherto been recognised—two such ‘rival’ theories must in fact agree on many claims that are clearly theoretical in nature. Given this, it is unclear how much of an impact on realism a demonstration that there is always an empirically equivalent ‘rival’ to any accepted theory would have—even if such a demonstration could be produced. Certainly in the case of the version of realism that I defend—structural realism—such a demonstration would have precisely no impact: two empirically equivalent theories are, according to structural realism, cognitively indistinguishable.

Defining disease: Much ado about nothing?

Medical science, of course, tries hard to characterise more definitely and fully the symptoms and causes of particular conditions generally referred to as diseases. Equally obviously, clinicians are called upon all the time to make diagnoses — to decide, against the background provided for them by the present state of medical science, and on the basis of their perceptions of the signs and symptoms, whether or not someone under their care has a particular condition: lung cancer, diabetes mellitus, congestive heart failure, or whatever. There is often a good deal of uncertainty about such judgments. Doctors strive hard to become more skilled at making them, and some philosophers — employing techniques from decision theory and artificial intelligence — have tried to help them. The topic of this paper, however, is not judgments of this sort, but rather of a second sort that medics are also sometimes called upon to make. These are second-level or meta-level judgments of the following kind: having identified some definite set of signs and symptoms, and being, let’s suppose, confident that they have diagnosed the correct condition, clinicians may then be called upon to decide whether or not that condition amounts to a genuine disease or illness. They often feel very uncomfortable about such judgments. Perhaps philosophers, with their expertise in conceptual matters, can provide significant help here by providing a clear-cut and defensible characterisation, not of any particular disease (that seems clearly a purely scientific issue), but of the class of diseases — of what might be called “disease-in-general.”

The pressure of light: The strange case of the vacillating ‘crucial experiment’

DOES A BEAM of light carry a momentum and hence exert a pressure on any absorbing or reflecting body on which it falls? This straightforward question seems to admit of a straightforward decision procedure: train a beam of light on a very mobile object and see whether it moves. And indeed, a series of investigators from the turn of the eighteenth to the beginning of the twentieth century performed experiments of precisely this kind. These experiments had much more than the usual share of importance; not only is the question of whether or not light exerts a pressure an intrinsically interesting one, it also seemed to be of the highest relevance for the comparative appraisal of two of the general theories of light current in the eighteenth and nineteenth centuries: the corpuscular theory and the wave theory. Indeed these pressure experiments seem, superficially at least, to be potentially crucial experiments for deciding between those two theories. In the first section of this paper I shall sketch the story of these experimental investigations. It is, as we shall see, full of fascinating twists and turns: both the experimental verdict and the supposed theoretical relevance of the verdict underwent more than one about-face. In the second section, I shall use this history to try to illustrate what I take to be important methodological lessons (about how science develops, about ‘crucial experiments’ and the role of experiments generally, and about the alleged ‘theory-ladenness’ of all observation statements).