Against utility
Authors: Jerome C. Wakefield
Journal: World Psychiatry (2016)

“The more palpable and practical the classification is, the better; if it cannot be perfect, let it be useful.”1 Jablensky's paper2 makes a compelling case that current psychiatric diagnostic categories fail to achieve full single-etiology construct validity as measured by the zones-of-rarity test, an important point that is broadly acknowledged. However, its further conclusions regarding utility as an alternative nosological goal are unwarranted. Defense of nosological proposals based on utility is a recipe for fruitless arguments detracting from pursuit of scientific grounding for diagnosis. This was a problem with the DSM-5 debates. Disputes about major proposals, such as elimination of the bereavement exclusion or adoption of the alternative DSM-5 model of personality disorder, that should have stayed focused on validity, strayed into swampy arguments about utility, obscuring crucial scientific issues. Jablensky's arguments do not support his conclusions. His pivotal point is the emphasis on zones of symptom rarity as the cardinal test of construct validity. The zones-of-rarity test, influentially put forward by Kendell and Jablensky3, has had momentous consequences for nosology: failure of current diagnostic categories to pass this test has supported the move towards dimensionalization that became one of DSM-5's signature goals, albeit one that was eventually mostly abandoned. For a doctrine of such importance, the zones-of-rarity test has been subject to surprisingly little critical discussion. Note that the test addresses more than just symptom discontinuities. Having initially focused on a zones-of-symptom-rarity test to evaluate typologies of depression, Kendell realized the limitations of this approach and expanded the allowable evidence of validity to include not just zones of symptom rarity revealing discontinuous symptom distributions, but also continuous symptom distributions that had discontinuous correlates with variables such as outcome, course, and treatment response4. This expanded approach was used in classic studies to argue that, for example, subthreshold depression is not categorically different from major depression. The problem with the zones-of-rarity test, however, is that, first, it gets wrong what is most essential in the quest for validly distinguishing disorders, namely, explanatory discontinuity, in which there are divergent etiologies (either one dysfunction versus another, or dysfunction versus normality); and second, it fallaciously assumes that such structural/explanatory discontinuities must be associated with superficial zone-of-rarity symptom/outcome discontinuities. Although zones of rarity suggest explanatory discontinuities, lack of such zones does not imply lack of explanatory discontinuity. As Kendell himself observed, “certainly, failure to demonstrate discontinuity in symptomatology can never prove that the conditions in question are not distinct entities”4. There are myriad scenarios in which divergent dysfunction etiologies would not manifest themselves in zones of symptom/outcome rarity. Function/dysfunction discontinuities may exist, but not be easily detectable against the normal-distribution background. Diagnostic criteria may mix indicators heavily overlapping with normality with other indicators that are more suggestive of pathology, so that discontinuities are obscured, a claim sometimes made about DSM major depression criteria. Significant numbers of false positives and false negatives on either side of a boundary can create the impression of continuity where none exists. A more substantive reason is that mental modules responsible for different facets of psychological processing are richly linked, and there is a great degree of mutual penetrability by mental systems due to their high need for coordination. Consequently, a dysfunction in one module is likely to create “comorbid” symptoms in interacting modules, as dysfunction-generated outputs act as deviant inputs to linked systems. This would tend to create the appearance of symptom continuity despite etiological heterogeneity. Additionally, the categorical distinction between dysfunction and normality can depend on very abstract theoretical considerations, such as the naturally selected range of a variable, and this abstract explanatory discontinuity may not be reflected in symptom or outcome distributions. So, for example, ability to detach at times from social rules may be adaptive as part of the social-relational repertoire, but if one has a strong tendency in that direction and this interacts with low levels of compensatory inhibitory and anxiety mechanisms, antisocial personality may result, and that may take the overall system outside the naturally selected range and undermine the biologically designed function of the social-relational mechanisms. Given the challenges of achieving validity, some argue that diagnostic revisions should be based on cost-benefit analysis, clinical utility, user acceptability, and whatever helps patients. Certainly such considerations should be carefully weighed, but only as an after-the-fact pragmatic supplement to validity, with validity the overriding arbiter in formulating diagnostic criteria. Utility and cost-benefit analysis involve subjective value judgments at their core. Opponents on both sides of DSM-5 debates cited utility and benefits to clients as warrants for their positions, without any clear way to adjudicate such claims, rhetorically obscuring validity issues. Judging utility rather than sticking to validity unduly inflates the moral pretensions of the profession. Attempts to define utility distinct from validity founder either on the Scylla of non-scientific triviality – because, once the “utility-as-separate-from-validity” door is opened, almost any idiosyncratic preference can come through it (e.g., user familiarity, reimbursement coverage) – or, if utility is defined more narrowly to make it diagnostically beneficial, the Charybdis of redundancy with partial validity. Relying on historical precedents for credibility, Jablensky's dichotomy has the latter problem, yielding a distinction without a difference. Jablensky cites P. Meehl as having originated his utility notion, but in the quoted passage Meehl is simply explaining the utility of having valid diagnoses as against not diagnosing at all, with Meehl's “utility” defined by the cardinal validity features of “etiological and prognostic homogeneity”5. Similarly, Kendell and Jablensky3 quoted R. Spitzer, but he actually equated clinical utility with validity and took both to reflect standard validity information about etiology, risk factors, course, family history, and response to treatment. Jablensky also cites Kraepelin's distinction between grouping disorders and establishing their pathological essence, but famously Kraepelin saw grouping as a path to validity. So, there is no support for a validity/utility distinction of fundamental nosological goals in these classic texts. Jablensky's own definitional attempt fares no better. He says we are seeking syndromes with “utility for predicting course, outcome and likely response to available treatments”, yet course, outcome, and response to treatment are intimately related to validity. Kraepelin famously used course and outcome to validate nosological distinctions, and Klein6 famously used comparisons of treatment response (“pharmacological dissection”) to reveal divergent diagnostic constructs and refine validity. So, Jablensky's claimed difference between validity and utility seems to be merely the difference between more and less perfect forms of validity. Jablensky's analysis makes the perfect the enemy of the good. He elevates the ideal goal of single-etiology validity to the only form of validity, when in fact validity is variegated, ranging from conceptual validity (successfully distinguishing normal vs. disordered conditions)7, through many forms of partial validity (marking various homogeneities among the dysfunctions underlying a domain of disorders), to single-etiology construct validity. Then, once validity is placed out of reach (and pushed further out of reach by the embrace of a spurious zone-of-rarity validity criterion), he argues for an alternative focus on utility. As my epigraph from a paper published in 18431 reflects, the idea that the difficulties in achieving validity in nosological classification should induce us to refocus on utility is not new. However, instead of “if it cannot be perfect, let it be useful”, I would suggest the motto “if diagnostic criteria cannot be perfectly valid, let them be as valid as possible”. That should be our goal, and in the long term it serves utility. Recent deployments of utility as a nosological rationale on both sides of various disputes suggest as well a paraphrase of W. James's comment about the unconscious8: utility “is the sovereign means for believing what one likes in psychology, and of turning what might become a science into a tumbling ground for whimsies”. Jerome C. Wakefield School of Social Work and Department of Psychiatry, New York University, New York, NY, USA