Coverage & Explainability

Art-market interpretation depends on what data is available, how reliable it is and how consistently it can be compared.

A market signal is never independent from its source context. A result from a major international auction house, a regional sale, a specialist sale, an online-only sale or a private-market reference may not carry the same meaning.

For this reason, Artmetria aims to make coverage visible, so users can understand not only what the platform says, but how much context supports it.

Coverage, on this page, is not a claim about how much of the art market Artmetria sees. It is a measurement of how much recorded evidence sits behind one published figure.

Each Index reading is computed over a rolling window of recorded sales — 90 days by default — and expressed against a reference window anchored in 2008. The number of sales that fall inside that window is what the coverage state describes. It is counted per market, not for the platform as a whole, so two readings shown side by side may rest on very different amounts of evidence.

Coverage being sufficient does not make a reading correct. It means the reading was computed on enough records to be worth arguing with.

Every Index reading carries one of four states, decided by how many recorded sales fall inside its window. The thresholds are fixed, and they are the same ones the platform applies internally:

• Canonical — 1,000 recorded sales or more in the window. The reading rests on a dense record.
• Under construction — at least 100 sales, but fewer than 1,000. The reading is published and should be treated as directional; precision improves as the record deepens.
• Provisional — the reference window is populated, but the qualitative dimension has not yet been computed across it. The figure reflects price and volume motion only, and says so.
• Insufficient — fewer than 100 sales. No Index value is displayed at all.

The last state is the one that matters most. Where the record is too thin to read, Artmetria does not publish a weaker number with a warning attached — it publishes nothing, and says why. A missing value here is a measurement, not an outage.

A canonical state does not mean perfect coverage. It means the segment is sufficiently recorded to be used responsibly.

Separately from its coverage state, each reading carries a confidence band derived from the same sample size:

• High — 1,000 recorded sales or more.
• Medium — 200 to 999.
• Low — 50 to 199. Read as indicative.
• Thin — fewer than 50. The window is widened before the value is shown at all.

A 95% confidence interval is published alongside the value itself, derived from the dispersion of prices in the window rather than assumed. A wide interval on a thin window is the honest output, and it is shown rather than rounded away.

Two adjustments exist because a sale calendar is uneven, and neither is silent.

The window can widen. When a 90-day window holds too few recorded sales to read honestly, the observation window is extended to 180 days rather than publishing a value computed on almost nothing. Thin sub-segments — a single period, a single region — reach that condition routinely. The reading records that its window was widened.

Coverage itself can move. A change between two periods can come from the market or from how much of it was recorded. When the number of sales in the current window differs by more than 30% from the comparison window, the reading is flagged for coverage drift — measured both against 90 days earlier and against the same period a year before. The flag does not correct the figure. It tells the reader that the variation may be describing the record rather than the market, which is a different statement and should not be read as the same one.

Some sources may be watched before they are fully indexed.

A house, fair, artist, sale calendar, event or publication may appear in Artmetria’s monitoring layer without being included in active scoring, Index outputs or automated recommendations.

This distinction matters.

Monitoring helps Artmetria identify relevant signals and future expansion areas. Indexing requires a higher level of data consistency, normalisation and methodological confidence.

Partial coverage means that Artmetria has some usable information, but not enough to treat a source, artist, segment or category as fully represented.

This may happen when:

• only some sales are available;
• lot-level information is incomplete;
• estimates or results are missing;
• historical depth is limited;
• source formats vary over time;
• image or provenance data is inconsistent;
• a category is too broad or too thin to compare reliably.

Partial coverage should not be read as absence of value. It means the available signal must be interpreted with caution.

The art market is uneven by nature.

Some regions have stronger public auction visibility. Others rely more heavily on galleries, private sales, fairs or informal networks.

Some categories produce frequent comparable records. Others are rare, episodic, highly specialised or dependent on expert attribution.

Artmetria’s coverage may therefore be stronger in some geographies, houses, periods or categories than in others.

This is not a failure of the method. It is a condition of responsible market interpretation.

Coverage affects how scores should be read.

A score supported by broad, consistent and recent data may carry a different level of confidence than a score based on limited, sparse or uneven information.

For this reason, Artmetria may use coverage notes, confidence indicators, data-quality warnings or source-context explanations where relevant.

A score is more useful when users can see the conditions under which it was produced.

Recommendations are also affected by coverage.

If an artist, category or region is only partially covered, Artmetria may still suggest it as an exploratory path, but such a recommendation should not be understood as a complete market assessment.

A recommendation may reflect aesthetic affinity, contextual relevance, visible market activity or educational interest. It does not mean that all relevant data has been captured.

Coverage also depends on access, rights and availability.

Some data may be public but inconsistent. Some information may be delayed, revised or removed. Some images or catalogues may not be reusable inside Artmetria.

Where source limitations exist, Artmetria aims to preserve caution rather than create false precision.

Coverage improves through several layers:

• adding new sources;
• deepening historical records;
• improving lot-level normalisation;
• refining categories and periods;
• strengthening artist matching;
• distinguishing active indexing from monitoring;
• adding confidence and data-quality indicators;
• learning from observed user behaviour.

The goal is not to pretend that the art market can be fully captured. The goal is to make the available signal clearer, more contextual and more responsibly interpreted.

If something is not covered, it should not be assumed to be unimportant.

If something is partially covered, it should not be treated as fully understood.

If something is actively covered, it should still be read within its category, source, region, date and confidence context.

Artmetria is designed to help users read market information more carefully, not to erase the complexity of the market itself.