Compare provider interfaces by the evidence they actually expose

Translate the research question into requirements

A macroeconomic vintage study needs revision and availability evidence. A country comparison needs indicator definitions, geography and consistent periods. A company balance-sheet study needs entity and accounting context. Write those requirements before comparing response speed or convenience, because the wrong subject cannot be repaired with a faster adapter.

The three fixture adapters illustrate these distinct contracts. They are technical demonstrations using invented values, not a recommendation that one provider is universally superior. The real provider documentation supports their broad interface roles; the fit criteria and examples below are this publication’s original evaluation framework.

A synthetic three-task matrix

Imagine tasks A, B and C. Task A asks for a daily-vintage macro series, task B for annual country indicators and task C for a company instant fact. Mark subject fit, period fit, availability evidence, revision identity and usage-rights evidence separately for each candidate interface.

For task A, a country indicator retrieved today does not become historically usable simply because its measured year is old. For task C, a macro series cannot replace a company-specific accounting fact. A matrix should mark unsupported requirements as unsupported, rather than averaging them into a high overall score because unrelated fields happen to be plentiful.

Make each mandatory criterion falsifiable. For example, require two retained versions of one observation with a documented selection rule, rather than accepting a provider page that merely uses the word historical.

Separate documented, demonstrated and operational

Documented means the provider describes a capability or field. Demonstrated means the retained fixture and adapter tests exercise a specific behavior. Operational means a real authorized integration has run in its intended environment with durable evidence. These statuses should occupy different columns.

For example, an offline fixture can demonstrate null handling and revision-key preservation without demonstrating live authentication, network access or current response latency. A provider’s documentation can describe bulk access without the publication having downloaded a bulk archive. Neither state should be relabeled as a live service offered by this site or by another research provider.

Compare failure and change behavior

Include pagination consistency, error shapes, rate-policy changes, schema drift and historical corrections. An integration that fails clearly on an unsupported field can be safer for a particular study than one that silently coerces the value. Document what happens when a required endpoint or metadata source becomes unavailable.

Use a synthetic acceptance scorecard with binary requirements where appropriate. If a study requires verified intraday availability and none of the selected fixture mappings supplies it, all candidates fail that requirement. Do not invent a numerical timestamp or weaken the requirement after seeing an otherwise attractive result.

Keep rights and operations in the final decision

A source can be technically suitable yet lack the permissions needed for the planned download or redistribution. Another can be lawfully reusable but lack the revision history needed for a historical replay. Record both conclusions without treating one as a substitute for the other.

The final selection note should state the exact interface version, request scope, accepted mapping, unresolved gaps and conditions requiring reevaluation. For the publication, those versions are FRED V1 observation fixtures, World Bank Indicators V2 annual fixtures and a bounded SEC company-facts instant fixture. Their normalization supports comparison of integration behavior, while preserving the differences that determine whether each can support a real research question.

Keep in the decision record

• Match the research question to subject, period and availability evidence.
• Keep documented, fixture-tested and operational capabilities separate.
• A missing mandatory requirement cannot be averaged away.

Source notes

1. FRED — API documentation, V1 and V2
2. World Bank — Indicators API Documentation, V2
3. SEC — Structured Data

Primary specifications support the interface descriptions. All downloadable response fixtures are synthetic. Access and rights checks are dated in the source inventory.

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