Validity, Reliability & Generalisability

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Internal validity (results true for study sample) vs external validity/generalisability (apply to other populations). Reliability/precision (reproducibility) vs validity (accuracy) — dartboard analogy diagram. Types of validity (face, content, construct, criterion). Random error vs systematic error. Intra-/inter-observer reliability, kappa (agreement beyond chance, >0.8 very good). Exam tip: precise but biased = reliably wrong.

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