Worked example 1
A nurse uses a 0–10 Numeric Rating Scale to assess post-operative pain. A patient rates pain as 3/10 but is observed grimacing and refusing to mobilise.
(a) Identify the measurement methods being used and one discrepancy between them. [3 marks] (b) Explain how the McGill Pain Questionnaire would provide additional information. [3 marks] (c) Evaluate the validity of self-report pain scales. [6 marks]
Show solution outline
(a) Methods and discrepancy:
- Self-report: NRS (0–10 numeric rating) — patient rates pain as 3/10 (mild).
- Behavioural observation: Grimacing and guarding/refusing mobilisation — suggests moderate-to-severe pain behaviour.
- Discrepancy: Self-report (3) underestimates pain compared to behavioural indicators — possible ** stoicism**, social desirability (not wanting to bother staff), or under-reporting due to opioid stigma.
(b) McGill Pain Questionnaire added value:
- Captures pain quality — sensory descriptors ("sharp," "throbbing"), affective ("sickening," "tiring"), evaluative ("annoying," "miserable").
- Would reveal whether patient experiences deep aching (surgical site) vs surface pain — guides analgesic choice.
- Present Pain Intensity subscale provides standardised intensity score comparable across patients.
(c) Evaluation of self-report validity:
- Strengths: Respects subjective nature of pain; VAS/NRS show good test–retest reliability in stable pain; sensitive to treatment change.
- Limitations:
- Social desirability — patients underreport to appear brave or avoid dependency label.
- Cultural variation — some cultures express pain openly, others stoically — same score may mean different experiences.
- Cognitive factors: Kahneman — peak-end rule means recall of pain depends on worst moment and most recent sensation, not average.
- No objective ground truth — cannot establish criterion validity against a gold standard.
- Children and non-verbal patients — self-report impossible; behavioural scales (FLACC, COMFORT) needed.
Judgement: Self-report is necessary but insufficient — combine NRS with behavioural observation and McGill for comprehensive assessment.