Names and aliases
exposure inequality, top-decile exposure share
Formula
qualified_exposure_of_top_decile_supply / total_qualified_exposure × 100%
Metric card
| Unit | % of all qualified exposure |
|---|---|
| Data source | Qualified impression events carrying a supply-unit identifier, eligible-supply snapshots, and a documented window definition. |
| Frequency | By micro-market and operational matching window; recompute whenever ranking logic changes. |
| Segments | micro-market, category, geography, seller cohort, ranking surface, query type |
Interpretation errors
- Treating any concentration as a defect: part of the inequality reflects genuine differences in relevance and quality.
- Comparing micro-markets with different eligible-supply sizes without normalisation.
- Reporting a single summary coefficient instead of the distribution curve and losing the shape of the tail.
Example
Illustrative example: the top 10% of supply units capture 58% of qualified exposure. The value is not a threshold and describes no real platform.
Use
Fix the decile definition and the window before analysis and keep both stable across compared periods. Publish the shape of the distribution alongside the value — at minimum the top-decile share, the median, and the zero-exposure share — because an identical concentration figure arises both from a smooth decline and from a gap between a small group and the rest of the market. Tie concentration to outcomes: if the top decile holds most exposure and returns a comparable share of qualified responses, allocation is working; if it does not, attention is being spent on units that do not convert it into matches.
Anti-example
Capping impressions for leading units lowers concentration without improving the market when the released exposure moves to units with a low qualified response rate. The metric looks better while the total number of matches may have fallen.
Limitations
- The metric describes a distribution without explaining it; ranking behaviour, demand structure, and supply quality produce indistinguishable concentration profiles.
- The top decile is a measurement convention rather than a property of the market, and it is unstable when eligible supply is small.
- No healthy level of concentration exists; the value is interpretable only as a trend within one micro-market under an unchanged definition.
Related metrics
exposure-coverage, zero-exposure-share, market-thickness, qualified-response-rate
Context sources
These works provide two-sided-market context; the formula above remains an author-defined working definition.
- Hanna Halaburda, Mikolaj Jan Piskorski, Pinar Yildirim. Competing by Restricting Choice: The Case of Matching Platforms (2017).
- Jun Li, Serguei Netessine. Higher Market Thickness Reduces Matching Rate in Online Platforms: Evidence from a Quasiexperiment (2019).