Conditions for Non-parametric Tests
Non-parametric tests require: random sampling, independent observations (for each test type), and that variables are measured on appropriate scales (usually ordinal or continuous).
Real World
A market research firm surveying customer satisfaction at Tesco uses ordinal Likert-scale ratings (1–5 stars), making non-parametric tests appropriate since the data are ranked categories rather than truly continuous measurements.
Exam Focus
When justifying test choice, name the specific assumption violated (e.g. 'data are ordinal') rather than just writing 'not normal'.
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