Diagnosis and classification: normality, abnormality and the DSM in diagnosing disorders (QCE Psychology Unit 2)
“Discriminate between adaptive and maladaptive behaviour; Discuss concepts of normality, including sociocultural, functional, historical, situational, medical and statistical approaches; Describe the concept of psychological disorder; Compare diagnostic manuals in common use, including the Diagnostic and Statistical Manual of Mental Disorders (5th edition-TR, 2022) and the International Classification of Diseases (11th revision, 2022), discussing the uses that different professions make of these manuals; Discuss the reliability and validity of diagnosis”
Abnormality is defined using approaches such as statistical infrequency, deviation from social norms, failure to function adequately and deviation from ideal mental health. Disorders are classified using systems such as the DSM-5 and ICD, interpreted through a biopsychosocial model. Diagnosis raises issues of reliability, validity, labelling and cultural bias, illustrated by Rosenhan's study.
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In the QCAA Psychology 2025 syllabus this subject matter sits in Unit 2: Individual behaviour, Topic 2: Diagnosis. Units 1 and 2 are the Year 11 foundation: QCAA says students should complete them before beginning Units 3 and 4, but they are not part of the Units 3 and 4 internal assessments or the external assessment. This page was previously filed under Unit 3.
What this dot point is asking
QCAA wants you to explain how psychologists decide what counts as normal or abnormal, describe the standardised systems used to classify and diagnose psychological disorders, and critically evaluate the problems with diagnosis. You should use named approaches, named classification systems and a named study.
The answer
Defining normality and abnormality
There is no single definition of abnormality; psychologists use several complementary approaches, each with limits.
- Statistical infrequency. Behaviour that is statistically rare is abnormal. The problem is that rare can also be desirable (high IQ), and common does not mean healthy.
- Deviation from social norms. Behaviour that violates a society's unwritten rules is abnormal. This is culturally and historically relative, and risks pathologising harmless difference.
- Failure to function adequately. Abnormality is the inability to cope with everyday demands (self-care, work, relationships). This is practical but subjective.
- Deviation from ideal mental health. Jahoda described criteria for ideal functioning such as self-actualisation and accurate perception of reality; by this strict standard almost everyone is abnormal at times.
Because each approach is flawed, clinicians use them together rather than relying on one.
Classification systems
To diagnose consistently, clinicians use standardised manuals.
- The DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, fifth edition), published by the American Psychiatric Association, lists disorders with specific diagnostic criteria. It is the dominant system in research and in Australia.
- The ICD (International Classification of Diseases), published by the World Health Organization, is used worldwide and includes mental as well as physical conditions.
These systems aim to make diagnosis reliable (different clinicians reach the same diagnosis) and to standardise communication, research and treatment.
The biopsychosocial model
Modern diagnosis interprets disorders through the biopsychosocial model, which holds that psychological disorders arise from an interaction of biological factors (genetics, neurochemistry), psychological factors (thoughts, learning, emotion) and social factors (family, culture, stress). This avoids reducing a disorder to a single cause and guides comprehensive treatment.
Issues with diagnosis
Diagnosis is essential but contested.
- Reliability and validity. A diagnosis is reliable if clinicians agree and valid if it identifies a genuine, distinct condition. Some categories show low inter-rater agreement, and high comorbidity (disorders co-occurring) raises questions about whether categories are truly distinct.
- Labelling and stigma. A diagnostic label can become a self-fulfilling prophecy and attract stigma.
- Rosenhan (1973), On being sane in insane places. Healthy pseudopatients gained admission to psychiatric hospitals by reporting a single hallucinated word, then behaved normally. Staff continued to interpret their normal behaviour through the diagnostic label, and none were detected as sane by staff. The study is a powerful critique of the reliability and validity of psychiatric diagnosis and of the power of labels.
- Cultural bias. Definitions of normality vary across cultures, so systems developed in one culture may misdiagnose people from another.
In Rosenhan's study, the pseudopatients were hospitalised for an average of around 19 days and all but one were discharged with a diagnosis of schizophrenia in remission, never recognised as sane by staff. This showed how a diagnostic label shapes how all later behaviour is interpreted.
State the claim and the system used
A clinician diagnoses a client with a disorder using the DSM-5 criteria. The exam task is to evaluate how trustworthy this diagnosis is, not to accept it at face value.
Apply reliability
Reliability asks whether different clinicians would reach the same diagnosis. Note that DSM-5 standardised criteria improve agreement, but some categories still show low inter-rater reliability and high comorbidity, which weakens confidence.
Apply validity and labelling
Validity asks whether the category identifies a genuine, distinct condition. Cite Rosenhan: healthy pseudopatients were diagnosed and their normal behaviour reinterpreted through the label, showing diagnosis can lack validity and that labels are self-perpetuating.
Add the cultural and biopsychosocial check
Conclude that definitions of normality are culturally relative, so a system built in one culture may misdiagnose another, and that a sound diagnosis interprets symptoms through the biopsychosocial model rather than assuming a single cause.
Putting it together for an exam
Name the definitional approaches and their limits, then name the classification system and the biopsychosocial framework, and finish with a critical evaluation citing Rosenhan and the concepts of reliability, validity and labelling.
- Relying on one definition of abnormality
- Each approach has weaknesses; strong answers combine several.
- Confusing the DSM and the ICD
- The DSM is the American Psychiatric Association's manual; the ICD is the World Health Organization's.
- Treating diagnosis as purely objective
- Rosenhan and the issue of cultural bias show diagnosis involves judgement and can be unreliable.
- Forgetting the biopsychosocial model
- Examiners reward explaining disorders as an interaction of biological, psychological and social factors rather than a single cause.
Exam-style questions
Questions in the style of QCAA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
2022 QCAA-style4 marksExplain two approaches psychologists use to define abnormality, and identify one limitation of each.Show worked answer →
Four marks: two approaches, each with a limitation.
Statistical infrequency (1 mark). Behaviour that is statistically rare is judged abnormal. Limitation (1 mark): rare can be desirable (a very high IQ), and common behaviour is not necessarily healthy.
Deviation from social norms (1 mark). Behaviour that breaks a society's unwritten rules is judged abnormal. Limitation (1 mark): norms are culturally and historically relative, so harmless difference risks being pathologised.
Other valid pairs include failure to function adequately (limitation: subjective) and deviation from ideal mental health (limitation: almost everyone falls short). Markers reward a clear approach with a genuine limitation, not a definition alone.
2023 QCAA-style6 marksUsing Rosenhan's (1973) study as evidence, evaluate the reliability and validity of psychiatric diagnosis.Show worked answer →
Six marks: the study described, then reliability and validity each evaluated with the evidence.
- The study (2 marks)
- Healthy pseudopatients were admitted to psychiatric hospitals after reporting a single hallucinated word, then behaved normally; staff continued to interpret their normal behaviour through the diagnostic label and none were detected as sane.
- Validity (2 marks)
- Diagnosing healthy people with schizophrenia, and discharging them as "in remission", questions whether the diagnosis identified a genuine condition (poor validity) and shows the power of labelling to distort interpretation.
- Reliability (2 marks)
- The study, alongside low inter-rater agreement and high comorbidity for some categories, raises doubts about whether clinicians consistently reach the same diagnosis. A balanced response notes modern manuals (DSM-5) have improved standardised criteria.
Markers reward the study as evidence linked explicitly to both reliability and validity.