---
title: "Variable dictionary, methodology, and citation policy"
method: GET
path: "/api/v1/research/maddison/definitions"
tags: ["Research"]
---

# Variable dictionary, methodology, and citation policy

`GET /api/v1/research/maddison/definitions`

Documentation endpoint for the Maddison Project Database. Returns the two variables (GDP per capita and population) with their units and methodology notes, the 8 regional slugs and their canonical names, the release metadata (version, DOI, DataverseNL URL), the CC BY 4.0 citation policy including the special rule requiring per-country source citations for analyses covering fewer than 12 countries, and a short and full academic citation string. Published by Bolt and van Zanden at the University of Groningen under CC BY 4.0.

## Response `200`

Variable dictionary, region list, methodology, and citation policy.

- EnvelopeMaddisonDefinitionsPayload
  - `data` MaddisonDefinitionsPayload, required — Variable dictionary, methodology notes, and citation policy.
    - `variables` MaddisonVariableRef[], required — Variables published by the Maddison Project Database.
      - `id` string, required — Stable variable identifier accepted by `/top?variable=`.
      - `label` string, nullable — Human-readable label for the variable.
      - `unit` string, required — Unit of measure.
      - `description` string, nullable — Methodology and interpretation notes for the variable.
    - `regions` MaddisonRegionRef[], required — Analytical regions used by MPD2023.
      - `slug` string, required — Stable slug accepted by `/regional?region=` (e.g. `western-europe`, `east-asia`).
      - `name` string, required — Region label as spelled in the upstream workbook.
    - `methodology` string, required — Methodology summary describing how GDP per capita and population are harmonised across centuries.
    - `citation_policy` string, required — CC BY 4.0 attribution policy including the special <12-country citation rule.
    - `citation_short` string, required — Short attribution string suitable for chart captions.
    - `citation_full` string, required — Full academic citation for the accompanying paper and dataset.
    - `release` MaddisonRelease, required — Release metadata for the loaded Maddison Project Database workbook.
      - `version` string, required — Release version identifier as published by the Maddison Project.
      - `doi` string, required — Digital Object Identifier for the DataverseNL dataset.
      - `published` string, required — Upstream publication date on DataverseNL (ISO 8601 UTC).
      - `url` string, required — DataverseNL landing page for the dataset.
      - `file` string, required — Source filename within the DataverseNL dataset.
    - `known_historical_codes_absorbed` string[], required — ISO-style codes for historical states absorbed into successor-state series (not shipped as separate rows by MPD2023).
  - `meta` SugraMeta, required — Metadata attached to every /api/v1/* response envelope.
    - `endpoint` string, required — Requested endpoint path.
    - `data_time` string, required — ISO 8601 UTC timestamp of the source data, not of the request.
    - `response_time` string, required — ISO 8601 UTC timestamp when this response was produced.
    - `provider` string, required — API name and version.
    - `source` string, nullable — Identifier of the primary upstream source used for this response.
    - `attribution` string, nullable — Human-readable attribution mandated by an upstream source (e.g. a securities regulator or self-regulatory organization). Present only on responses whose source requires the owner and source to be clearly identified. Do not remove or alter it when using the response.
    - `fallback_used` boolean, nullable — True when the primary source failed and a fallback produced the data.
    - `fallback_chain` string[], nullable — Ordered list of sources attempted, in the order they were tried.
    - `cached` boolean, nullable — True when this response was served from the internal cache.
    - `stale` boolean, nullable — True when the cached response was returned after the upstream rate-limited or errored. Clients can use this to detect degraded data.

## Other responses

- `401` — Missing or invalid `x-api-key` header. JSON body with a stable `code` distinguishing `missing_api_key` (no header sent) from `invalid_api_key` (header sent, key not accepted); any other 401 source carries the generic `unauthorized` with its detail as `reason`. Plus `hint`. `plan` is always null on 401 - an unauthenticated request has no plan; quota exhaustion is 429, not 401.
- `429` — Daily rate limit exceeded. Check `X-RateLimit-Reset` for the next window.
- `503` — Upstream source is temporarily unavailable. Retry after a short delay.

---

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