Sharing a unit is necessary but not sufficient for two figures to be comparable. Currency and nominal/real basis, data vintage, the underlying definition, geography and boundary, and index base period all have to match. When in doubt, treat figures as benchmarks to read alongside one another rather than as directly equivalent values.
- Same unit is not enough — basis, vintage, and definition must match too.
- Prices are benchmarks, not equivalences.
- See per-unit notes at /units.
Same currency and basis
USD figures are comparable only with other USD figures on the same nominal-or-real basis. Never compare a nominal value to a real one, or across currencies without conversion.
Same year vintage
GDP shares and deflated values depend on the data vintage; compare only figures computed against the same base year and methodology revision.
Same definition
Two values in the same unit (e.g. 'million b/d') are comparable only if the underlying product and boundary definitions match — crude vs total liquids are not interchangeable.
Same geography & boundary
Country or region totals must share the same territorial definition and inclusion rules before they can be compared.
Benchmarks, not equivalences
Market prices are benchmarks; two benchmark prices in USD/bbl track different grades and delivery points and are not directly equivalent.
Index base periods
Index values are comparable only within the same index and base period; re-based indices are not directly comparable.
Related
Units reference: /units · data dictionary: /data-dictionary · style guide: /methodology/style-guide.