Methodology

v1.0 · Published 2026-04-18

Prediction.Markets is the neutral reference layer for the prediction market category. This document describes how every number on this site is computed, updated, and corrected.

1. Sources

We ingest public order books and trade feeds from Kalshi, Polymarket, and Limitless. Snapshots refresh every 60 seconds during market hours, every 10 minutes overnight, and immediately on resolution. We do not use private APIs, non-public data, or any data that venues have not made publicly accessible.

2. Consensus calculation

Volume-weighted aggregation across venues. For each event, we compute the weighted midpoint price across all venue snapshots, weighted by 24-hour trading volume. Outlier venues are flagged — not dropped — when their price deviates more than 2 standard deviations from the weighted mean. All venue prices are always surfaced in the venues table; only the consensus number uses the weighted calculation.

3. AI Oracle lineup

Three frontier models — Claude Opus 4.7 (Anthropic), GPT-5 (OpenAI), and Grok 4 (xAI) — produce independent probability forecasts via OpenRouter on a daily cadence for political/macro markets, and every 4 hours for sports/culture during active windows. Each model receives the same prompt: the resolution criteria, current consensus price, and recent news context. Models output structured JSON: probability (0–1), a short thesis (≤140 chars), a long thesis (≤600 chars), and key drivers.

4. Forecast journal

Every Oracle forecast is written to an append-only, immutable Postgres table. Forecasts are never deleted or overwritten. Revisions are logged as new rows with a reference to the prior forecast. The full journal is accessible via API from launch.

5. Scoring — Brier score

Forecasts are scored using the Brier score: (forecast − outcome)². Lower is better; 0 is perfect. We always display the sample size alongside the score: 'Claude: 0.142 Brier (7 resolved markets).' The score is honest about being sparse at launch.

6. Movement feed

We surface: trades larger than $10k USD, probability jumps greater than 3pp within 5 minutes, Oracle revisions of 5pp or more, and matched news items via keyword and entity extraction. All movement events are timestamped and logged.

7. Resolution

Markets resolve when the underlying venue resolves. If venues disagree, we hold the market until majority agreement. We publish all back-tests and do not retroactively alter resolved forecasts.

8. Corrections policy

If we identify an error in our process, we log a public correction entry rather than silently overwriting data. To report an error, email corrections@prediction.markets. We aim to respond within 24 hours and publish corrections within 72 hours of confirmation.

9. What we're not doing yet

The Oracle does not yet have persistent memory across events. Models do not see each other's forecasts. We do not yet model venue-specific liquidity risk in consensus weighting. These are scheduled for v2.