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Before anyone can be treated for a mental disorder, someone has to decide that they have one — and that decision rests on an answer to a deceptively simple question: what makes a behaviour or state of mind "abnormal"? The previous lesson showed that the line between normal and disordered has moved across history; this lesson examines the four formal attempts psychologists use to draw that line today, and then turns to the machinery that puts those judgements into practice: the diagnostic classification systems (DSM and ICD) and the vexed questions of whether diagnosis is reliable (consistent) and valid (accurate). We close by characterising three families of disorder — an affective (mood) disorder, a psychotic disorder, and an anxiety disorder — so that the abstractions have concrete referents. Every part of this lesson feeds directly into Rosenhan's study, which is essentially a demonstration of what happens when diagnosis goes wrong.
| This lesson covers | OCR H567 Component 03, Section A topic | AO focus |
|---|---|---|
| Statistical infrequency; deviation from social norms; failure to function adequately; deviation from ideal mental health | Issues in mental health — defining abnormality (Background) | AO1; AO3 strengths/limitations of each definition |
| Classification systems: DSM and ICD | Categorising disorders | AO1; AO2 applying criteria |
| Reliability and validity of diagnosis | Categorising disorders — issues in diagnosis | AO3 evaluation |
| Characteristics of an affective, a psychotic and an anxiety disorder | Characteristics of categories of disorder | AO1; AO2 recognising symptoms |
The specification is referenced descriptively throughout; consult the official OCR H567 specification document for the exact published wording. This lesson develops AO1 (defining the four definitions and describing disorder characteristics), AO2 (applying definitions and diagnostic criteria to novel cases) and AO3 (evaluating the strengths and limitations of each definition and of the diagnostic process itself).
Psychologists have proposed several ways of deciding when something crosses the line into "abnormal". None is fully satisfactory on its own; each captures part of the truth and misses part. Examiners reward candidates who can state each definition precisely, illustrate it, and — crucially — weigh its strengths against its limitations.
The statistical infrequency definition says a behaviour or characteristic is abnormal when it is statistically rare — when it lies far from the average in a population. If we plot a measurable trait (say, IQ) it typically forms a normal distribution, a bell-shaped curve with most people clustered around the mean and progressively fewer at the extremes. On this view, "abnormal" simply means unusual: a person with an IQ below 70 is statistically abnormal because very few people score that low, and this figure is indeed used in defining intellectual disability.
Strengths. It is objective and quantifiable — once you have a cut-off, deciding who falls outside it is a matter of measurement, not opinion. It has genuine clinical uses, for example in diagnosing intellectual disability.
Limitations. It cannot distinguish desirable from undesirable rarity: a genius-level IQ is just as statistically infrequent as a very low one, yet we would never call it a disorder. It gives no guidance on where to set the cut-off (why 70 and not 75?). And many disorders are not rare at all — depression is common — so statistical infrequency would perversely classify a widespread disorder as "normal".
The deviation from social norms definition says a behaviour is abnormal when it violates the unwritten rules — the moral and social standards — of a society. Every culture has expectations about how people should behave; conduct that breaches them (talking to people who are not there, extreme antisocial behaviour, gross disregard for others' safety) may be judged abnormal. The clinical concept of antisocial personality disorder, which involves persistent violation of others' rights, leans on this idea.
Strengths. It captures the genuinely social dimension of abnormality that a purely statistical view misses — disorder often shows up as a breach of what a community expects.
Limitations. Social norms are relative to time and place, so this definition can pathologise mere nonconformity and has been abused to label the socially inconvenient as ill (recall homosexuality's former classification, or drapetomania). It risks becoming a tool of social control rather than care, and it depends on context — behaviour normal at a football match is deviant in a library.
The failure to function adequately definition focuses on the individual's ability to cope with the ordinary demands of daily life — to hold down work, maintain relationships, care for oneself, and get through the day without excessive distress. When a person can no longer do these things, or is causing distress to themselves or others, they may be judged abnormal. Rosenhan and Seligman proposed features that signal such failure, including personal distress, maladaptive behaviour, unpredictability, irrationality and observer discomfort.
Strengths. It centres the person's own experience and distress, which matters clinically — people often seek help precisely because they can no longer function. It is practical, focusing on observable, real-world impact.
Limitations. "Adequate functioning" is culturally and normatively loaded — who decides what counts as coping, and by whose standards? Some people function outwardly while suffering greatly; others live unconventionally (a hermit, an eccentric artist) without any disorder. And some serious conditions, in their early stages, do not obviously impair functioning.
The deviation from ideal mental health definition, associated with Marie Jahoda (1958), turns the question around: instead of asking what is wrong, it asks what psychological health looks like and treats abnormality as its absence. Jahoda proposed criteria for ideal mental health, including a positive self-attitude (self-esteem), self-actualisation (realising one's potential), autonomy, accurate perception of reality, resistance to stress, and mastery of the environment. Anyone falling short on these is, by this definition, deviating from ideal health.
Strengths. It is positive and holistic, defining health in its own right rather than merely as the absence of illness, and it aligns with humanistic ideas about growth and potential (which you will meet later in this section).
Limitations. Its criteria are so demanding that almost everyone fails to meet them all at once, which would make the whole population "abnormal". The criteria are heavily culturally biased toward individualist, Western values (autonomy and self-actualisation are prized very differently in collectivist cultures), and "ideal mental health" is far harder to measure objectively than physical health.
| Definition | Core idea | Key strength | Key limitation |
|---|---|---|---|
| Statistical infrequency | Rare = abnormal | Objective, quantifiable | Rare can be desirable; common disorders missed |
| Deviation from social norms | Breaks social rules | Captures social dimension | Relative; enables social control |
| Failure to function adequately | Cannot cope with daily life | Centres distress; practical | "Adequate" is normatively loaded |
| Deviation from ideal mental health | Falls short of ideal health | Positive, holistic | Almost everyone fails; culturally biased |
A sophisticated conclusion notes that these definitions are best used together: a person is most confidently judged disordered when their state is unusual, breaches social expectations, impairs functioning and departs from psychological health. Any single criterion, used alone, produces absurd results.
It is worth dwelling on why this problem resists a clean solution, because the difficulty is itself examinable. Each definition, examined closely, smuggles in a value judgement that it cannot justify from within. Statistical infrequency pretends to be purely descriptive — just counting who is rare — but the moment we ask which rare traits count as disorders, we have to import a judgement about which deviations are bad, and that judgement comes from outside the statistics. Deviation from social norms wears its evaluative character on its sleeve, but that honesty is also its danger, because it makes "abnormal" mean little more than "disapproved of", which is exactly how psychiatry has historically been abused. Failure to function looks pragmatic and person-centred, but "adequate functioning" is defined against a background expectation of how a life should go, and those expectations are culturally and historically specific — a life of contemplative withdrawal that one society honours, another pathologises. Deviation from ideal mental health is the most openly normative of all, since it begins by stipulating what a good mind looks like. The deep lesson is that abnormality is not a natural boundary waiting to be measured, like the freezing point of water; it is a line drawn by human judgement, and every definition is an attempt to make that judgement look objective. This does not mean the concept is useless — people really do suffer and really do need help — but it means that a diagnosis is always partly a decision, and that humility about where the line falls is intellectually honest rather than evasive.
A further theme, which connects directly to Rosenhan, is that a diagnosis is not a neutral description but an act with consequences. On the positive side, a label can bring enormous relief and practical benefit: it gives a frightening experience a name, it tells the sufferer they are not alone and not to blame, it opens the door to treatment and support, and it lets clinicians communicate and researchers accumulate knowledge. Many people describe their diagnosis as the moment their suffering was finally taken seriously. On the negative side, a label can stigmatise, inviting others to see the person through the diagnosis rather than as an individual; it can become self-fulfilling, as the person begins to interpret their own ordinary reactions as symptoms; and, as Rosenhan will show, it can prove sticky, colouring how everything the person subsequently does is perceived. The same label is therefore simultaneously a key and a cage. A mature understanding of classification holds both truths at once, and recognises that the goal of good diagnostic practice is to capture the genuine benefits while guarding against the harms — which is one reason reliability and validity matter so much, since an unreliable or invalid label inflicts the harms without earning the benefits.
One more conceptual point sharpens the evaluation of DSM and ICD. A classification system is best thought of as a map of the territory of human distress, and like any map it involves simplification, choices about where to draw boundaries, and a purpose. The dominant manuals draw categorical boundaries — you either meet the criteria for a disorder or you do not — which has the practical virtue of yielding clear decisions, but distress in reality often comes in degrees and blends rather than discrete boxes, which is part of why comorbidity and symptom overlap are so common. An alternative, dimensional, approach would rate people along continua (of, say, anxiety or low mood) rather than sorting them into categories, and many researchers argue this better fits the data. Understanding that the categorical structure is a choice — a useful one, but not the only possible one, and one inherited from Kraepelin — is exactly the kind of critical perspective that distinguishes an A-Level answer from a textbook summary. It also frames the next lesson: Rosenhan's pseudopatients exploited the categorical system's confidence that "sane" and "insane" are clean, separable boxes.
Deciding that something is wrong is only the start; clinicians must then classify which disorder a person has, so that they can communicate, plan treatment and conduct research. Two great manuals do this work.
It is worth pausing on why classification is necessary at all, since the whole apparatus of manuals and criteria can seem bureaucratic until one asks what the alternative would be. Without an agreed system of categories, every clinician would be an island: there would be no shared language in which a psychiatrist in one city could describe a patient to a colleague in another and be confident they meant the same thing, no way to accumulate research (since "depression" in one study might mean something quite different from "depression" in the next), and no basis for matching a treatment shown to work for a condition to a new patient said to have that condition. Classification is, in short, the precondition for psychiatry to be a cumulative, communicable enterprise rather than a collection of individual impressions. That is the powerful case for the manuals, and it should be given its due before the criticisms are pressed. The criticisms — that the categories may be invalid, culturally biased, or harmful in their effects — are real and serious, but they are best understood as arguments for improving classification, not for abandoning it, since the practical need the manuals meet does not go away.
The DSM — the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association, currently in its fifth edition (DSM-5, with a text revision) — is dominant in the United States and in research. The ICD — the International Classification of Diseases, published by the World Health Organization and now in its eleventh revision (ICD-11) — is used worldwide and covers all diseases, with a chapter on mental and behavioural disorders. Both list disorders, describe their characteristic symptoms, and specify how many symptoms, and for how long, are needed for a diagnosis. They are the direct descendants of Kraepelin's classificatory project introduced in the previous lesson.
The manuals matter because they attempt to make diagnosis systematic: rather than each clinician judging by instinct, they match a patient's presentation against explicit criteria. This is what makes psychiatric diagnosis look like medical diagnosis. But the whole enterprise rests on two questions that the classification systems must satisfy — and that critics say they do not fully meet.
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