{
  "index_name": "Concentration / Pump Risk",
  "short_name": "HHI",
  "as_of": "2026-05-12",
  "snapshot_note": "Per-market Herfindahl-Hirschman Index across all resolved Polymarket markets with at least 20 matches. HHI close to 1 means a single wallet drove most participation; close to 0 means activity was diffuse. High HHI is the precondition under which one trader can mechanically move the consensus price, not direct evidence that they did.",
  "methodology": "For each market, compute each wallet's share of total participation events (each match contributes one event for the maker and one for the taker). HHI = sum(share^2). Threshold cutpoints 0.25 / 0.50 / 0.75 map onto the DOJ horizontal-merger-guideline categories (unconcentrated, moderately concentrated, highly concentrated). Markets with fewer than 20 matches (=40 participations) are excluded to avoid trivial HHI=1 from sparse activity. Material-activity top-markets table requires >=100 matches.",
  "population": {
    "n_markets_eligible": 229771,
    "min_matches_per_eligible_market": 20,
    "total_participations_in_eligible_markets": 548148748.0,
    "summary_stats": {
      "mean_hhi": 0.05623631779053161,
      "median_hhi": 0.043704474505723206,
      "p90_hhi": 0.10739795918367347,
      "p99_hhi": 0.25144246395180797,
      "mean_top_wallet_share": 0.13790247892677546,
      "median_top_wallet_share": 0.1206896551724138
    }
  },
  "thresholds": [
    {
      "min_hhi": 0.25,
      "n_markets": 2331,
      "share_of_eligible": 0.010144883383890918,
      "participations_in_flagged_markets": 788122
    },
    {
      "min_hhi": 0.5,
      "n_markets": 30,
      "share_of_eligible": 0.00013056477971545583,
      "participations_in_flagged_markets": 1960
    },
    {
      "min_hhi": 0.75,
      "n_markets": 0,
      "share_of_eligible": 0.0,
      "participations_in_flagged_markets": 0
    }
  ],
  "hhi_histogram": [
    {
      "bin_low": 0.0,
      "n_markets": 202566,
      "participations": 537151126
    },
    {
      "bin_low": 0.1,
      "n_markets": 22798,
      "participations": 9541238
    },
    {
      "bin_low": 0.2,
      "n_markets": 3068,
      "participations": 1022784
    },
    {
      "bin_low": 0.3,
      "n_markets": 987,
      "participations": 295822
    },
    {
      "bin_low": 0.4,
      "n_markets": 322,
      "participations": 135818
    },
    {
      "bin_low": 0.5,
      "n_markets": 30,
      "participations": 1960
    }
  ],
  "top_markets": [
    {
      "market_id": "1297729",
      "total_participations": 1022,
      "hhi": 0.49804879730086815,
      "top_wallet_share": 0.49902152641878667,
      "n_unique_wallets": 3
    },
    {
      "market_id": "1305375",
      "total_participations": 568,
      "hhi": 0.4930569331481849,
      "top_wallet_share": 0.5,
      "n_unique_wallets": 3
    },
    {
      "market_id": "618093",
      "total_participations": 602,
      "hhi": 0.4835653028112272,
      "top_wallet_share": 0.49169435215946844,
      "n_unique_wallets": 10
    },
    {
      "market_id": "1300622",
      "total_participations": 4936,
      "hhi": 0.4727367680705248,
      "top_wallet_share": 0.4977714748784441,
      "n_unique_wallets": 13
    },
    {
      "market_id": "1287901",
      "total_participations": 2774,
      "hhi": 0.4716774727111208,
      "top_wallet_share": 0.4863013698630137,
      "n_unique_wallets": 31
    },
    {
      "market_id": "1308902",
      "total_participations": 540,
      "hhi": 0.47107681755829905,
      "top_wallet_share": 0.4925925925925926,
      "n_unique_wallets": 10
    },
    {
      "market_id": "1246323",
      "total_participations": 378,
      "hhi": 0.4693457629965566,
      "top_wallet_share": 0.5,
      "n_unique_wallets": 14
    },
    {
      "market_id": "1308633",
      "total_participations": 1746,
      "hhi": 0.46917122954250523,
      "top_wallet_share": 0.48911798396334477,
      "n_unique_wallets": 28
    },
    {
      "market_id": "1300617",
      "total_participations": 6510,
      "hhi": 0.46487219237330724,
      "top_wallet_share": 0.49923195084485406,
      "n_unique_wallets": 12
    },
    {
      "market_id": "1305391",
      "total_participations": 1216,
      "hhi": 0.46467467754501374,
      "top_wallet_share": 0.48355263157894735,
      "n_unique_wallets": 15
    },
    {
      "market_id": "617081",
      "total_participations": 376,
      "hhi": 0.46361475780896333,
      "top_wallet_share": 0.48404255319148937,
      "n_unique_wallets": 13
    },
    {
      "market_id": "694236",
      "total_participations": 688,
      "hhi": 0.46306280421849655,
      "top_wallet_share": 0.48401162790697677,
      "n_unique_wallets": 17
    },
    {
      "market_id": "584251",
      "total_participations": 298,
      "hhi": 0.4608125760100895,
      "top_wallet_share": 0.4798657718120805,
      "n_unique_wallets": 10
    },
    {
      "market_id": "1131203",
      "total_participations": 2028,
      "hhi": 0.45438758758057807,
      "top_wallet_share": 0.47731755424063116,
      "n_unique_wallets": 34
    },
    {
      "market_id": "606553",
      "total_participations": 364,
      "hhi": 0.4528589542325806,
      "top_wallet_share": 0.49175824175824173,
      "n_unique_wallets": 8
    },
    {
      "market_id": "1307050",
      "total_participations": 638,
      "hhi": 0.4513713505173888,
      "top_wallet_share": 0.47962382445141066,
      "n_unique_wallets": 19
    },
    {
      "market_id": "1304494",
      "total_participations": 862,
      "hhi": 0.4497230312067657,
      "top_wallet_share": 0.4802784222737819,
      "n_unique_wallets": 16
    },
    {
      "market_id": "941331",
      "total_participations": 5996,
      "hhi": 0.44966257246881514,
      "top_wallet_share": 0.4743162108072048,
      "n_unique_wallets": 34
    },
    {
      "market_id": "1308962",
      "total_participations": 922,
      "hhi": 0.4491367911876944,
      "top_wallet_share": 0.49023861171366595,
      "n_unique_wallets": 9
    },
    {
      "market_id": "1287899",
      "total_participations": 1442,
      "hhi": 0.4487901108223476,
      "top_wallet_share": 0.47434119278779474,
      "n_unique_wallets": 42
    }
  ],
  "interpretation_caveats": [
    "High HHI is necessary but not sufficient for single-trader price manipulation. A market with HHI = 1.0 (one wallet on both sides of every match) might be a venue-operator test market, an early-launch bootstrap, a tiny niche market with one dedicated trader, or actual manipulation.",
    "Algorithmic market makers can drive a single market's HHI above 0.5 simply by providing most of the liquidity. The flag is on the market structure, not on the intent of the dominant wallet.",
    "The HHI here is on participation count, not dollar volume. A wallet that places many small trades will weigh more in HHI than a wallet that places a few large trades. A volume-weighted variant is a candidate v2 refinement."
  ],
  "generated_at": "2026-05-12T07:58:26+00:00",
  "source": "J:/Research/10. Prediction/data/blockchain/processed_trades.csv",
  "wallclock_seconds": 6916
}