Schizophrenia

A Scientific Delusion?

Mary Boyle

• Editorial: Routledge
• Año: 2014
• ISBN:
  9781317797838
• Edición: 2
• Categoría: Medicina
• Categoría: Teoría, práctica y referencia médicas

First published in 2002. Schizophrenia: A Scientific Delusion?, first published in 1990, made a very significant contribution to the debates on the concepts of schizophrenia and mental illness. These concepts remain both influential and controversial and this new updated second edition provides an incisive critical analysis of the debates over the last decade. As well as providing updated versions of the historical and scientific arguments against the concept of schizophrenia which formed the basis of the first edition, Boyle covers significant new material relevant to today's debates.

Chapter 1

Evaluating the validity of ‘schizophrenia’

Two major claims have been made about the concept of schizophrenia: first, that it is a scientific concept or, at least, that those who use it work within a scientific framework (for example, Gottesman and Shields, 1982; Wing, 1988; APA, 1994; Sartorius, 1994; Ross and Pam, 1995) and, second, that the term refers to a particular kind of medical pattern known as a syndrome (Gottesman and Shields, 1982; Kendell, 1991; APA, 1994). These claims imply that the concept has been developed and is used in a manner similar to that of other concepts which claim scientific status and that the phenomena to which it refers are similar to those usually denoted by the medical term ‘syndrome’. This chapter will describe in detail what is meant by these claims, not least because their meaning is rarely spelt out and is often misrepresented in the literature, but also as a necessary prelude to evaluating whether the introduction, development and use of the concept of schizophrenia actually conforms to the claims made about it.

‘Schizophrenia’ as a scientific concept

As Medawar (1984) and Chalmers (1990) have pointed out, attempts to define ‘science’, to give the term some absolute meaning, have always ended in failure. With this in mind, all that will be attempted here is a description of some of the ways in which those who call themselves scientists – particularly natural and medical scientists, with whom supporters of ‘schizophrenia have identified themselves – tend to proceed. This rather pragmatic stance, however, should not be thought of as second best: the crucial issue is that, given the claims made about ‘schizophrenia’, then the ways it has been developed and used ought at least to be recognisable to philosophers and practitioners of natural and medical science. Kendell (1991), a supporter of ‘schizophrenia’, concurs, claiming that ‘[the concept of schizophrenia] can only be judged by the same criteria as other explanatory concepts’ (60).

The search for patterns and attempts to describe relationships between phenomena are fundamental to scientific activity. They are central, too, to much non-scientific activity; of particular interest here is that they are central to lay or everyday attempts to understand behaviour and other events. What perhaps distinguishes the two is the scientist’s persistent demand for the provision of certain types of evidence that a pattern has been observed and the imposition of various publicly demonstrable criteria for evaluating it. This demand for evidence, and its public evaluation, is crucial in view of our apparent propensity to claim that certain events ‘go together’, in the absence of any direct evidence that this is the case (see, for example, Shweder, 1977; Chapman and Chapman, 1982).

Observables and unobservables in scientific theory

Scientific theories contain both observables and unobservables. The term ‘observable’ can give the misleading impression of referring to some outside reality, but I am using it here simply to mean readily agreed statements about sense data with a minimum of interpretation. In scientific research, simple statements about putative relationships between observables (when certain metals are brought close together, one moves towards the other) are used to justify inferring unobservables (magnetic force); as we shall see, these unobservables are then used to aid the construction of more elaborate theoretical statements.

It is readily agreed that ‘schizophrenia’ is an unobservable, an abstract concept inferred from overt behaviour or from verbal reports of behaviour and experience (Kendell, 1991; APA, 1994). Scientific theories, however, may contain different types of unobservables and it is important to distinguish them in assessing the validity of ‘schizophrenia’. Beck (1953) has distinguished two types of unobservables by applying the concepts of systemic and real ‘existence’ and the language of logic to differentiate them. The first, he says, is that ‘mode of existence of an (unobserved) entity all descriptions of which are analytical within a system of propositions’, while real existence ‘is the mode of existence attributed to an entity if there is any true synthetic proposition that can be made about it’ (369). In other words, statements about an unobservable said to have real existence will contain words which are not reducible to the empirical relationships from which it is inferred and will imply hypotheses about the antecedents of these empirical relationships.

Benjamin (1937) has made the same distinction by contrasting what he calls abstractive and hypothetical methods in scientific activity. In the abstractive method, phenomena are grouped by a restrictive set of properties into classes whose relationship can be discovered empirically; nothing is added to what is observed. By contrast, the hypothetical method relates observations by ‘inventing a fictitious substance or process or idea in terms of which the experiences can be expressed. It correlates observations by adding something to them’ (184). Constructs formed by Benjamin’s abstractive method (e.g. solubility, resistance, temperature, habit strength; hunger as X hours of food deprivation, and so on) would be said by Beck to have systemic existence, while those formed by the hypothetical method (electricity; proton; intelligence; diabetes) would be said to have real existence. MacCorquodale and Meehl (1948) have suggested the terms ‘intervening variables’ and ‘hypothetical constructs’ to distinguish these two types of unobservables, and these terms (with ‘construct’ and ‘concept’ used interchangeably) will be adopted here. Other names have, however, been suggested: Beck uses constructions and inferred entities, while Carnap (1937) uses the term ‘dispositional concepts’ rather than ‘intervening variables’. Although all hypothetical concepts refer to unobservables, it is worth noting a distinction between two different types. The first is that which becomes, in Beck’s phrase, an ‘object of search’ and which is postulated by scientists to show certain characteristics. The constructs of atom or proton are examples of this type; although unobserved at the moment, they are claimed to exist as a result of certain observations and mathematical calculations and may be observed at some future point, given appropriate technology. The second type of unobservable remains for ever an abstraction, which cannot be postulated to exist except in the most abstract sense. ‘Intelligence’, ‘memory’, ‘diabetes’ and ‘multiple sclerosis’ are examples of this type of hypothetical construct.

Which kind of concept is ‘schizophrenia’? Kraepelin clearly did not see his concept of dementia praecox, from which the modern concept of schizophrenia is derived, as being reducible to a statement about correlations between behaviours. Instead, he postulated a ‘metabolic disorder’ to account for the putative correlations. Similarly, statements made today about the concept contain terms not reducible to statements about behavioural correlations. ‘Schizophrenia’ is said to be an illness; a biochemical disorder; a genetic disorder. What is implied by statements like these is not always specified but it is clear that something is being added to a statement about behavioural correlations. ‘Schizophrenia’ therefore functions as a hypothetical construct rather than an intervening variable; and, as an abstraction from observables, rather than an ‘entity’ postulated to exist as a result of observations, it also functions as one of the second type of hypothetical construct – no one ever expects to ‘see’ schizophrenia, any more than they expect to ‘see’ diabetes, regardless of how advanced technology becomes. It must be emphasised that this status as an eternal abstraction is perfectly respectable and has nothing to do with the present lack of a clear relationship between biochemical events and behaviour said to be symptomatic of schizophrenia. Even if such events were to be observed in the future, the concept of schizophrenia would remain an abstraction because there is no identity between it and any biological, genetic or behavioural event, any more than there is identity between the concept of diabetes and a specific biological event.

The most important distinction between hypothetical constructs (of both types) and intervening variables lies in the predictive function of hypothetical constructs (Benjamin, 1937; MacCorquodale and Meehl, 1948; Beck, 1953; Carnap, 1974). They have, or should have, the power to generate predictions about events which have not yet been observed. This power derives partly from the fact that hypothetical constructs, unlike intervening variables, are not reducible to statements about what has already been observed, but imply hypotheses about the antecedents of what has been observed. This distinction has important implications for evaluating the validity of the two types of construct. The validity of an intervening variable can be questioned only by denying the observations from which it was originally inferred, i.e. by claiming that such and such did not actually happen. The concept of solubility, for example, requires only that substances be observed to dissolve at different rates and to different extents in water or other liquids; it implies nothing about the variables which control this. These observations are therefore said to be both necessary and sufficient conditions for asserting the validity of the concept. For a hypothetical construct, the actual occurrence of the empirical relationships from which it was inferred is, of course, a necessary condition for asserting its validity, but it is not sufficient. The demonstration of predictive power is central to assertions of the validity of hypothetical constructs and is the sufficient condition for inferring them.

The correspondence rules of hypothetical constructs

To say that a construct has predictive power is to say that it is capable of predicting events which, though observable in principle, have not yet been observed. Thus, the concept of intelligence may be capable of predicting performance differences in a laboratory task. It is possible to use unobservables to make and investigate statements about observables because of what are variously called correspondence rules (Carnap, 1974), operational rules (Bridgman, 1927) and The Dictionary (Campbell, 1920; cited in Carnap, 1974). These rules, which may be very simple or highly complex, specify what must be observed before a concept can be inferred and may specify quantitatively the relationship between variation in what is observed and variation in the inferred construct. The correspondence rules for the concept of intelligence, for example, specify the relationship between observable responses to items on a standardised test and ‘amounts’ of the unobservable concept, intelligence. Any investigation of the predictive power of a hypothetical construct therefore involves examining the relationship between two sets of observables.

The process of change of correspondence rules

Inferred constructs usually start as relatively vague concepts associated with certain observations. It is then discovered, by empirical investigation, that these observations vary systematically with another observation which can be made more reliably and is more strongly correlated with relevant experimental changes. The concept of temperature, for example, was originally associated with global, subjective judgements of hot and cold. It was later shown that these judgements and a range of other phenomena were reliably correlated with measurable changes in the height of a mercury column. The correspondence rules for inferred constructs (i.e. what must be observed before the construct is inferred) therefore change over time as a result of increasing specification and elaboration of events which can be shown to be associated with the original set of observations from which the construct was inferred. That correspondence rules do change in this way may of course demonstrate a construct’s predictive power.

This process of change in correspondence rules is well illustrated by the development of the medical concept of diabetes mellitus. The construct of diabetes was originally inferred by the Greeks from observations of the co-occurrence of inordinate thirst and urine production, lethargy and emaciation. These observations therefore constituted the first set of correspondence rules for the hypothetical construct of diabetes. In the seventeenth century it was noted that this cluster was frequently and reliably associated with sweet-tasting urine. Thus, a new correspondence rule could be set up between an observable event and the unobservable ‘diabetes’. Later, it was discovered that sweet-tasting urine contained glucose which could be detected independently of the original observation of inordinate thirst, and so on, or judgements about the sweetness of urine. Yet another set of correspondence rules could therefore be set up. These, in turn, were superseded by rules specifying that diabetes mellitus was to be inferred when a certain relationship between intake of glucose and its level in the blood at certain time intervals was observed. (The ‘division’ of the concept of diabetes into mellitus and insipidus was necessitated by the observations that inordinate thirst and urine production were not always associated with sweet-tasting urine and, later, that they could be associated with low levels of anti-diuretic hormone.)

Every attempt to examine the fate of predictions from a hypothetical construct involves the use of its correspondence rules. Each attempt to show that the sufficient conditions for inferring the construct are fulfilled therefore involves invoking the necessary conditions for inferring its existence. In the very early stages of a construct’s development, the necessary conditions – the putative regularities from which the construct was originally inferred – will also be the correspondence rules. Later, the necessary conditions will be invoked indirectly as the correspondence rules change. But it would be quite wrong to depict this process of change in correspondence rules as one of finding out what a hypothetical construct ‘is’. Young (1951) and Carnap (1974) have noted how often the question, ‘What is X?’, where X is a hypothetical construct, is put to scientists by lay people. They point out that the question is unanswerable and is based on a misunderstanding of the function of hypothetical constructs. These concepts can only be described in terms of the observed events from which they are inferred and the predictions which have been made from them, in terms, that is, of the theoretical network in which they are embedded. The question ‘What is diabetes?’ would be answered (and attempts, however misguided, are often made to answer such questions) very differently in classical Greece and in the modern Western world and will, no doubt, be answered very differently again in the twenty-second century as the theoretical network is further elaborated. Each answer is ‘true’ but misleading; to pose the question at all is to reify the construct and to imply that there is a final, concrete answer.

Deriving predictions from hypothetical constructs

The correspondence rules which tie unobservable to observable events provide the general means for examining predictions from a construct. The content of these predictions can be specified only by examining the whole theoretical network which surrounds the concept, the assumptions on which it is based, indeed, everything that is asserted about it (Cronbach and Meehl, 1955). The statements which make up this network may relate observables to each other, unobservables to observables, and/or unobservables to one another. But it is axiomatic that any construct which claims scientific status be embedded in a network in which at least some of its statements contain observables. The ease with which researchers can derive predictions from this network, and then investigate them, depends not on its simplicity but on its specificity. One obvious result of a lack of specificity is disagreement over the content of predictions; another is disagreement over the results of attempts to test an agreed prediction. There is no question of a concept’s validity depending on a particular number of the predictions derived from it being upheld; there is certainly no quantitative answer to the question, ‘How valid is construct X?’ Rather, validity is usually assessed from a utilitarian stance by asking in what ways and for what purposes the construct has proved useful. The term ‘utility’ is therefore often used instead of ‘validity’ to reflect the fact that, as a rule, a hypothetical construct has no claim to validity unless it can be used to predict events which, without the construct, would probably have gone undetected. If the same events are predicted by different constructs, then that which carries fewest assumptions is usually preferred.

It may happen, however, that research fails to detect events predicted from a construct. The question then arises of whether the ‘fault’ lies with the construct, and its theoretical network, or with the method of inquiry. As will be seen in Chapter 2, the nineteenth-century medical profession sought to retain the concept of mental disease even though they were unable to detect the predicted differences between the brains of those said to be mentally diseased and the brains of those who were not. It was argued that existing methods of measuring brain function were not sufficiently advanced to detect the postulated differences. This may well have been true, but such a post hoc argument could be used indefinitely to justify the continued use of a concept, one of whose major predictions had no empirical support. It can be argued instead that if a construct has already led to the detection of previously unobserved events and if it predicts specific events observable in principle but undetectable by existing methods, then the failure to detect such an event might well indicate that a more sophisticated methodology is required and not that the construct is invalid. But if a concept is in the early stages of development, if it lacks a history of ‘successful’ predictions or is embedded in a loose theoretical network which cannot be used to predict specific events, then the ‘failure’ of a major prediction should direct attention to the concept itself. In particular, such failures should direct our attention to the fundamental question of whether the necessary condition for inferring the concept has been fulfilled; that is, was a set of regularities which would justify bringing the concept into existence ever observed? The question is crucial, as this necessary condition is invoked, directly or indirectly, every time a prediction is ‘tested’. This failure to make reliable predictions to new observations, being embedded in a loose and ever-changing theoretical network and failing to specify what would be observed were technology to improve, is precisely the problem which besets the concept of schizophrenia (Bentall, 1990b; Boyle, 1994; British Psychological Society, 2000). The question, then, of whether the necessary conditions for inferring schizophrenia have been fulfilled – of whether anyone has ever observed a pattern of regularities which would justify the original and continued existence of the concept – will be central to this book.

Lay and scientific concepts

These methods of developing and investigating constructs can be compared with the development and use of what are often called ‘lay’ or ‘folk’ concepts. Our language is rich in terms, particularly those referring to people, which are superficially similar to hypothetical constructs. Some of them (deep; hard) are obviously metaphorical and others (anxious; normal) less obviously so. There are some major differences between these concepts and those whose claims to scientific status are rarely disputed; two of these are of particular interest here. The first is that the correspondence rules of lay concepts are often many and varied, and vary from user to user. They also tend to change in idiosyncratic ways over time: the referents of the concept ‘nice’, for example, used to be very similar, when applied to women, to those of later concepts like ‘fast’. The second difference is that, although these terms may appear to be derived from patterns of behaviour, no systematic attempts are usually made to check this; or, when they have been made (for example, Shweder, 1977; Kahneman et al., 1982) the apparent patterns have been shown to be more closely related to cultural beliefs about ‘what goes with ...