Ps in a POD – definitions in circles

Ps in a POD – definitions in circles

In my paper “The Disunity of Evidence-Based Medicine“, I lay out four distinct definitional strategies employed by proponents of Evidence-Based Medicine, each conveniently beginning with P: Platitude, Paradigm, Principles and Process. I made a bad pun about “Ps in a Pod” in a section title, which actually originates with some content that I cut, which doubles down on the bad pun to quite an absurd extent. However, there’s an underlying point to be made which is missing in the paper because that section didn’t make it in: namely, that having four established definitions with different properties and focuses gives EBM proponents a really useful – and really, really frustrating – rhetorical strategy. This strategy was the POD, otherwise known as the ‘Point of Defence’ strategy. Understanding the way this strategy works helps us to see why EBM is so easily inoculated against critics. I share an edited version of this omitted section below:


A major challenge often addressed to EBM proponents is to spell out explicitly the process or principles they defend. The relationship between the ‘Four Ps’ allows an escape from these challenges, in the form of what I call the ‘Point of Defence’ (POD) strategy. Call the definition of EBM being defended at a particular time the ‘Point of Defence’. As we have seen, each of the Four Ps can be challenged—platitudinous definitions are challenged to explicate the difference between EBM and non-EBM interpretations of ‘best evidence’ (What’s new?); principles and process definitions are challenged to explicate the practical implementation of their principles (How?) or the theoretical justification behind the steps in the process (Why?), respectively; and paradigm definitions can be challenged as vague and ambiguous (What’s believed? What’s done?), and moreover as requiring explication of the distinctive features of the ‘EBM paradigm’.

In each case, it is possible to deflect or avoid the challenge by moving the POD from one type of definition to another. For instance, questions about the justification for the EBM process are deflected by shifting the POD to a Principles definition, while questions about the practical application of the principles can be avoided by moving the POD to a Process definition. Similarly, the distinctive features of the EBM paradigm, or the interpretation of ‘best evidence’ in the EBM platitude can be fleshed out by changing the POD to a Process or Principles definition. Moreover, if the underlying justification for certain EBM Principles are challenged, the proponent can roll back the POD to a Paradigm definition in order to assert that, like a paradigm, these principles must simply be accepted as constituting the foundation of clinical practice.

Indeed, different versions of the same type of EBM definition can be employed in subtly moving the POD. For example, one could defend Guyatt et al.’s two principles from criticism by moving the POD to the five “linked ideas”—the hierarchical principle is insulated from criticism by deferring to ideas (1) and (3). The emptiness of these ideas is then defended by moving to the Process definition, and the specifics of the process are explicated by moving back to Guyatt et al.’s hierarchical principle, completing the slow loop.

Such a strategy results in a continual circulation between EBM definitions ad nauseum. Criticisms of each POD are deflected or avoided by moving to a different POD. Although systematic accounts of this strategy have not been described in the critical literature previously, many critics of EBM have lamented this strategy—EBM proponents are often accused of retreating and deflecting criticism, and even of intellectual dishonesty for the deliberate adoption of such tactics to insulate their position from criticism.

This strategy might be defended by arguing that the definitions are not circular. Each definition (with the exception of the platitude, which is unlikely to feature) adds new information. At least the first circulation between definitions is ampliative. In particular, the Principles and Process approaches add significantly in response to challenges to the Paradigm definition. We learn about what’s believed and what’s done by practitioners within the EBM paradigm. Similarly, the Principles and Process definitions seem to support one another—the principles provide some theoretical justification for the process, while the process provides an approach to practical implementation of the principles.

However, even if the POD strategy is not a circular definition, it is not really a definitional strategy at all. Rather, POD strategies are attempts to avoid giving a definition. A circular definition unpacks one term by using another which is then ultimately unpacked using that first term—or alternatively unpacks a term by using the term itself. By contrast, the POD strategy does not result in such a statement—no single definition is taken as fundamental and clarified by using the other ‘definition’ types. For example, if the Platitude is taken as fundamental, the POD strategy does not, as a definitional strategy would, focus upon unpacking key terms such as “best evidence”, but rather responds to challenges to unpack terms by making entirely different statements of the form ‘EBM is…’—‘EBM is a set of principles’, ‘EBM is a new paradigm’, ‘EBM is a process performed by practitioners’, etc. The POD strategy cannot be circular, then, because there is no definitional or clarificatory relationship between the processes, principles, paradigm and platitude. The POD strategy, then, is not a definition of EBM, but a rhetorical strategy to avoid plumping for a single definition which must then be clarified and can then be attacked.

A more sophisticated strategy is to adopt pluralism about Evidence-Based Medicine. In pluralism, a number of different definitions are all accepted as (equally) legitimate. Here, a pluralist view would hold that ‘EBM’ means several different things in different contexts—EBM is a set of principles, but it also is a paradigm for clinical practice and a process which clinicians perform. There is no single definition of ‘Evidence-Based Medicine’, because EBM refers to a number of different things depending on the context in which it is used.

However, this pluralistic strategy suffers from a number of problems—indeed, it takes on all of the challenges made to each of the types of definition. If a pluralistic approach holds that one of the things EBM is is a new paradigm for clinical practice, then this part of the definition can be challenged: is clinical practice paradigm based? Is EBM really a new paradigm? What does that paradigm commit its adherents to? Equally, if EBM is a set of principles, we can challenge EBM proponents to explicate these principles clearly and draw out their practical implications, if there are any. If EBM is a process for clinical practice, we can demand the justification for this particular process, and clarification of the steps involved. Pluralism inherits the problems of each monistic definition included. Moreover, pluralism seems an unattractive proposition for EBM proponents—surely EBM proponents call their process, principles and paradigm by the same name because of some relationship between them. These are not meant to be independent concepts which happen to bear the same name. The EBM process is meant to be justified by the ideas and principles of EBM, and the paradigm is meant to commit adherents to the particular process and principles.

I suggest that, rather than accepting a number of competing definitions as legitimate and allowing EBM proponents to move between these definitions and avoid criticism of each, we adopt a different characterisation of Evidence-Based Medicine. ‘EBM’ is not a single set of ideas and practices—many similar but non-identical ideas and practices fly under the same banner. I argue that EBM is best characterised as a social movement within medicine.


For the argument that EBM is best characterised as a social movement, and what that means for philosophers interested in EBM, you can read “The Disunity of Evidence-Based Medicine“.