System: Young horses in marathon handicap chases

Mechanism and rationale

Chases of three and a half miles or more are thought to need an old, hardened horse, so the young ones are let go at bigger prices than they deserve. Aged seven or under they have won more often than their prices implied in every period since 2020; older horses in the same races have not.

The rule

race_type = 'Chase' AND is_handicap = 1 AND age <= 7 AND distance_yards >= 6160

Reads: race_type, is_handicap, age, distance_yards

Pre-registration

Spec hash (sha256 of the canonical pre-spec)

not designed yet

Frozen

not frozen

The definition can still change.

Backing

bookmaker

Kind

system

Live from

2026-10-13

Matched

{
  "hypothesis_id": "H175-young-horse-in-a-marathon-chase",
  "similarity": 1,
  "variant": "handicap"
}

Published

true

Rules

• The race is a handicap chase over three and a half miles or further.
• The horse is seven years old or younger.

Source

Age and stamina analysis, October 2026

System id

young-stayer-marathon-handicap-chase

Tier

none

Where

race_type = 'Chase' AND is_handicap = 1 AND age <= 7 AND distance_yards >= 6160

Discovery result

Not measured yet.

Falsification

No attacks yet. Only promising ideas are attacked.

Sealed holdout (vault)

Not queried. Only a frozen idea can spend its one query against the 2020-25 holdout.

Forward record

No forward record. Shadow tracking starts after the vault and counts only races run after the freeze.

Lineage

Agent runs

• investigator v1ok · 46s · 16 Oct, 13:43

  Output (schema-checked)

  {
    "reflection": "H175 began as a NEGATIVE idea: young horses (7 or under) in chases of 3m4f or more would be over-bet because the market assumes an improver will stay. The numbers came out the other way. Discovery gave A/E 1.128 on 289 bets, and the broad import gave A/E 1.16 on 618 (BSP ROI +10.1%). The handicap subset was GREEN at 1.181 on 584 and is now live as SYS-young-stayer-marathon-handicap-chase. By LEARNINGS rule 10 this reversal is a discovery: the market seems to under-rate young horses at marathon trips, probably because the 'needs an old, hardened horse' idea is common knowledge and gets priced in too hard. Two warnings. First, the edge is fading by period (1.17, 1.21, then 1.05 on 125), so the latest period is barely above break-even. Second, the reversed mechanism has never been tested directly. We don't know whether the lift comes from youth itself, from being unexposed at the trip, from a dose-response with distance, or from something else that young marathon runners share, such as large-field festival handicaps or low weights. The live system needs a mechanism check before more forward bets are trusted.",
    "answers": [],
    "questions": [
      {
        "question": "Is the young-stayer lift carried by horses that have not yet run at 3m4f+ (stepping up in trip), as the 'market doubts unproven stamina' mechanism requires?",
        "rationale": "If the reversed mechanism is right, the mispricing should sit with runners whose stamina is unknown, not with young horses already proven at the trip. Columns: last_distance_yards, st_3m_runs, st_placed_3m, chase_runs, prior_runs, age, distance_yards. A clear split would confirm or undercut the live system's story.",
        "observation_ids": [
          "O-f49a1279"
        ],
        "priority": 0.7
      },
      {
        "question": "Do big-field festival marathon handicaps (Nationals and similar) produce the lift, rather than youth?",
        "rationale": "Marathon handicap chases are dominated by a few large, competitive, high-overround races, where longshot pricing behaves differently. Columns: field_size, book_pct, course, race_class, sp_decimal. If the lift disappears in ordinary-sized fields, the system is a race-type effect.",
        "observation_ids": [
          "O-f49a1279"
        ],
        "priority": 0.6
      },
      {
        "question": "Does the edge fall away as the trip shortens (a dose-response from 3m to 3m4f+), as a stamina-doubt mechanism predicts?",
        "rationale": "If the market's error is doubt about whether a young horse stays, the error should shrink at shorter trips where staying is less in question. Columns: distance_yards, age, race_type, is_handicap.",
        "observation_ids": [
          "O-f49a1279"
        ],
        "priority": 0.5
      },
      {
        "question": "Is the third-period fade (A/E 1.05 on 125) the market catching up, or just noise on a small sample?",
        "rationale": "The live system's forward value depends on whether the edge is decaying. Read forward bets on SYS-young-stayer-marathon-handicap-chase by period and by sp_decimal band.",
        "observation_ids": [
          "O-f49a1279"
        ],
        "priority": 0.45
      }
    ],
    "hypotheses": [
      {
        "title": "Young marathon chasers stepping up to 3m4f+ for the first time carry the lift",
        "family": "age-stamina",
        "operator": "test-mechanism",
        "question_id": null,
        "new_question": 0,
        "parent_id": "H175-young-horse-in-a-marathon-chase",
        "reasoning": {
          "observation_ids": [
            "O-f49a1279"
          ],
          "question": "Is the lift concentrated in young horses whose stamina for a marathon trip is not yet proven?",
          "mechanism": "Young chasers are often still improving and have more stamina than their form at shorter trips shows. Punters and layers lean on the belief that a marathon needs a seasoned horse, so a young horse stepping up in trip is doubted most.",
          "market_miss": "The form book shows only runs at shorter trips, often finishing one-paced or beaten. Those runs make the horse look short of stamina at exactly the moment the longer trip suits it.",
          "prediction": {
            "direction": "positive",
            "size": "A/E 1.15 to 1.30 on 250+ bets, above young runners already raced at 3m4f+",
            "falsified_if": "A/E at or below 1.05, or no higher than young runners whose last run was already at 3m4f+"
          },
          "rule_sketch": "race_type = 'Chase' AND is_handicap = 1 AND age <= 7 AND distance_yards >= 6160 AND last_distance_yards < 6160"
        },
        "confounders": [
          "field size",
          "festival handicaps",
          "weight carried",
          "trainer concentration"
        ],
        "expected_survival": 0.4
      },
      {
        "title": "Rival: big-field festival marathon handicaps, not youth, produce the lift",
        "family": "age-stamina",
        "operator": "rival-explanation",
        "question_id": null,
        "new_question": 1,
        "parent_id": "H175-young-horse-in-a-marathon-chase",
        "reasoning": {
          "observation_ids": [
            "O-f49a1279"
          ],
          "question": "Does the young-stayer edge survive outside large-field marathon handicaps?",
          "mechanism": "If youth is the cause, young horses should beat their prices in ordinary-sized marathon handicaps too. If the cause is the longshot pricing of big festival fields, the effect should disappear in small fields.",
          "market_miss": "In large, high-overround fields, young unexposed runners drift with the rest of the outsiders. In small fields that pricing distortion is weaker.",
          "prediction": {
            "direction": "positive",
            "size": "A/E 1.08 to 1.20 on 200+ bets in fields of 13 or fewer",
            "falsified_if": "A/E at or below 1.0 in fields of 13 or fewer, which would rule the rival in"
          },
          "rule_sketch": "race_type = 'Chase' AND is_handicap = 1 AND age <= 7 AND distance_yards >= 6160 AND field_size <= 13"
        },
        "confounders": [
          "race class",
          "course",
          "book_pct",
          "price band"
        ],
        "expected_survival": 0.45
      },
      {
        "title": "Dose-response: young handicap chasers at 3m to 3m3f show a smaller lift",
        "family": "age-stamina",
        "operator": "generalise",
        "question_id": null,
        "new_question": 2,
        "parent_id": "H175-young-horse-in-a-marathon-chase",
        "reasoning": {
          "observation_ids": [
            "O-f49a1279"
          ],
          "question": "Does the edge shrink as the trip gets shorter, as a stamina-doubt mechanism requires?",
          "mechanism": "The market's doubt about a young horse's stamina should grow with distance. At 3m to 3m3f a young horse should still be slightly underrated, but less than at 3m4f+.",
          "market_miss": "The 'young horses don't stay' heuristic applies more weakly at standard staying trips, so the mispricing should be smaller but still present.",
          "prediction": {
            "direction": "positive",
            "size": "A/E 1.03 to 1.10 on 800+ bets, below the 1.18 seen at 3m4f+",
            "falsified_if": "A/E at or above the 3m4f+ figure (no gradient), or at or below 0.97"
          },
          "rule_sketch": "race_type = 'Chase' AND is_handicap = 1 AND age <= 7 AND distance_yards >= 5280 AND distance_yards < 6160"
        },
        "confounders": [
          "novice handicaps",
          "race class",
          "field size"
        ],
        "expected_survival": 0.35
      }
    ],
    "findings": [
      {
        "statement": "H175 was framed as negative (young marathon chasers over-bet) but came out positive: A/E 1.16 on 618, BSP ROI +10.1%. The live system therefore rests on a reversed, untested mechanism.",
        "kind": "fails",
        "observation_ids": [
          "O-f49a1279"
        ]
      },
      {
        "statement": "The young-stayer edge weakens in the latest period (1.17, 1.21, then 1.05 on 125), so the live system's forward bets should be checked for decay before more weight is placed on it.",
        "kind": "method",
        "observation_ids": [
          "O-f49a1279"
        ]
      }
    ]
  }

Timeline

1. hypothesis note SYS-young-stayer-marathon-handicap-chase

   15 Oct, 23:10 · importer

2. New idea SYS-young-stayer-marathon-handicap-chase: System: Young horses in marathon handicap chases (import)

   15 Oct, 23:10 · importer

Every change is an event with an actor: an agent and its version, an engine, a human, or the importer. Current stage: Live.