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9990 · 1.2.1

Diagnostic criteria for mood (affective) disorders — practice questions

Practice and worked examples for 9990 Diagnostic criteria for mood (affective) disorders. Short previews only — attempt the full question in MarkScheme against the official scheme.

Worked example 1

For three weeks, a student reports low mood every day, has stopped hobbies they once enjoyed, sleeps 12 hours nightly, feels worthless, and cannot concentrate on revision.

(a) Apply DSM-5 criteria to explain why this may be diagnosed as major depressive disorder. [4 marks] (b) Evaluate the validity of diagnosing mood disorders using classification systems. [6 marks]

Show solution outline

(a) AO1 — Applying DSM-5 criteria:

  • Core symptoms: Depressed mood daily + anhedonia (stopped hobbies).
  • Additional symptoms (≥3): Hypersomnia, feelings of worthlessness, poor concentration.
  • Total: Five+ symptoms present.
  • Duration: At least two weeks (three weeks here); causes functional impairment (revision affected).

(b) AO3 — Validity evaluation:

  • Strengths: Standardised criteria improve reliability across clinicians; distinguish clinical depression from transient sadness.
  • Limitations — medicalisation: Horwitz & Wakefield argue normal grief may meet criteria — false positive risk.
  • Cultural validity: Depression may present as somatic complaints in some cultures — Western mood-focused criteria may under-diagnose or misclassify.
  • Comorbidity: Overlap with anxiety, substance use — unclear whether categories reflect distinct disorders or shared underlying dimension.

Judgement: DSM-5 criteria offer useful operational definition but validity depends on context — clinician must assess proportionality, culture, and impairment, not symptom checklist alone.

Worked example 2

A clinician uses the Patient Health Questionnaire-9 (PHQ-9), a common screening tool, to assess a patient's symptoms over the last two weeks. The patient scores each of the 9 items on a scale from 0 ('Not at all') to 3 ('Nearly every day'). The scores are as follows:

  • Little interest or pleasure: 3
  • Feeling down, depressed: 3
  • Trouble sleeping: 2
  • Feeling tired: 2
  • Poor appetite: 1
  • Feeling bad about self: 2
  • Trouble concentrating: 2
  • Moving/speaking slowly: 0
  • Thoughts of self-harm: 1

(a) Calculate the patient's total PHQ-9 score. [2 marks] (b) Using the standard severity thresholds (5-9: Mild, 10-14: Moderate, 15-19: Moderately Severe, 20-27: Severe), interpret this score and explain why it does not constitute a formal diagnosis on its own. [4 marks]

Show solution outline

(a) AO2 — Calculation of PHQ-9 Score:

  • Step 1: Sum the scores for all 9 items.
  • Formula: Total Score = Σ(Item 1 to Item 9)
  • Working: 3 + 3 + 2 + 2 + 1 + 2 + 2 + 0 + 1 = 16.
  • Final Answer: The patient's total PHQ-9 score is 16. [2 marks]

(b) AO3 — Interpretation and Evaluation:

  • Interpretation: A score of 16 falls within the 'Moderately Severe' range of depressive symptoms (15-19). This indicates a significant level of symptomatology that is likely causing distress and impairment.
  • Why not a diagnosis? The PHQ-9 is a screening tool, not a diagnostic instrument. While the score strongly suggests MDD, a formal diagnosis requires a full clinical interview to:
    1. Confirm the duration (≥2 weeks) and consistency of symptoms.
    2. Assess for 'clinically significant distress or impairment' in functioning (e.g., at work, in relationships).
    3. Rule out other causes, such as a substance, a medical condition, or another psychiatric disorder (e.g., bipolar disorder).
    4. The PHQ-9 score provides a quantitative measure of symptom severity, but the clinician's judgement is needed to apply the full DSM-5 criteria. [4 marks]
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