Part 4 · Biostatistics and Research Methods

28. Data, Variables and Scales of Measurement

~2 min read

Same concept, other depth: Foundation →

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Scale	Properties	Permissible statistics	Examples
Nominal	Categories, no order	Frequencies, %, mode; chi‑square	Sex, blood group, religion, HTN yes/no (binary)
Ordinal	Ordered; unequal intervals	Median, percentiles, ranks; non‑parametric tests	Education level, SES class, pain scale, cancer stage, smoking status (if ordered)
Interval	Equal intervals; arbitrary zero	Mean, SD; parametric tests; no ratios	Temperature °C, calendar year, IQ
Ratio	Equal intervals; true zero	All of the above plus ratios, geometric mean, CV	Age, BMI, BP, Hb, pack‑years, income

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Scale

Properties

Permissible statistics

Examples

Nominal

Categories, no order

Frequencies, %, mode; chi‑square

Sex, blood group, religion, HTN yes/no (binary)

Ordinal

Ordered; unequal intervals

Median, percentiles, ranks; non‑parametric tests

Education level, SES class, pain scale, cancer stage, smoking status (if ordered)

Interval

Equal intervals; arbitrary zero

Mean, SD; parametric tests; no ratios

Temperature °C, calendar year, IQ

Ratio

Equal intervals; true zero

All of the above plus ratios, geometric mean, CV

Age, BMI, BP, Hb, pack‑years, income