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The same indicator can be published in different units by different countries, and the API reports what the publisher actually published rather than forcing a conversion that would misstate the source. Read unit on every row. It is the field most often skipped and the one that causes the most damage when it is.

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Units

Never compare or average across units. An unemployment rate in percent and payrolls in thousands are both labour market indicators and are not commensurable. Pooling them produces a number with no meaning.

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Index levels are not comparable across countries

An index is defined against a base period chosen by its publisher. Two countries’ indices at 114 are not “the same”; they are each 14% above whatever their own base was. Compare changes in index levels, never levels themselves.

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Periods

periodStart and periodEnd bound what the reading covers. frequency names the cadence. Periods are reported as the publisher defines them. A quarterly row ending 2026-06-30 covers April to June, whatever the country’s fiscal convention.

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Seasonal adjustment

Where a publisher offers both, the API prefers the seasonally adjusted series, because that is what the same figure means when compared across months. Mixing adjusted and unadjusted readings within one series produces artificial swings that look like real economic movement. The API does not do this, and neither should a pipeline that joins across sources.

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Revisions

Official statistics are revised. A figure fetched today may differ from the same period fetched last month, and that is the publisher correcting itself, not the API changing its mind. For point in time work, store releaseDate alongside every value and reconstruct what was known on a given date rather than assuming today’s history was always today’s history.