{
  "certificate_version": "1",
  "record": {
    "schema": "fraud-temporal/1",
    "archetype": "claim_vs_effect",
    "issued_at": "2026-09-16T19:18:25.823336+00:00",
    "subject": {
      "model": "xgboost (production-configured, scale_pos_weight)",
      "dataset": "ULB MLG 'Credit Card Fraud Detection' (284,807 anonymized European card transactions, Sept 2013)",
      "rows": 284807,
      "fraud_rate": 0.0017,
      "split": "time-sorted 50/50 (train on earlier transactions, test on later)",
      "trained_on": "earlier transactions (first ~50% by time)",
      "deployed_on": "later transactions (last ~50% by time)"
    },
    "claim": "the model achieves a stable validated accuracy",
    "verdict": "falsified",
    "finding": {
      "gap": "temporal_drift",
      "effect": "f1 swings 0.538 to 0.857 across time segments (1.59x spread) \u2014 the validated number is a snapshot, not a property",
      "detail": "fraud rate and model performance genuinely drift over time, so a model validated on an earlier window is a moving target when deployed on later transactions"
    },
    "per_segment": {
      "0": {
        "n": 17850,
        "fraud_rate": 0.0049,
        "recall": 0.8276,
        "f1": 0.8324
      },
      "1": {
        "n": 17851,
        "fraud_rate": 0.0004,
        "recall": 0.8571,
        "f1": 0.5455
      },
      "2": {
        "n": 17851,
        "fraud_rate": 0.0011,
        "recall": 0.7368,
        "f1": 0.6364
      },
      "3": {
        "n": 17850,
        "fraud_rate": 0.0009,
        "recall": 0.8125,
        "f1": 0.7027
      },
      "4": {
        "n": 17850,
        "fraud_rate": 0.0013,
        "recall": 0.8261,
        "f1": 0.7451
      },
      "5": {
        "n": 17852,
        "fraud_rate": 0.0018,
        "recall": 0.8438,
        "f1": 0.8571
      },
      "6": {
        "n": 17850,
        "fraud_rate": 0.0015,
        "recall": 0.7778,
        "f1": 0.8077
      },
      "7": {
        "n": 17853,
        "fraud_rate": 0.0007,
        "recall": 0.5833,
        "f1": 0.5385
      }
    },
    "record_hash": "9d02588f47b6ff18be738f57ed14a4f646a42529a2ab2c8a9ef0a78b1fa5bf27"
  },
  "signature": {
    "algorithm": "ed25519",
    "key_id": "5d303baa00a6b243",
    "verifier_version": "0.2.0",
    "signed_hash": "9d02588f47b6ff18be738f57ed14a4f646a42529a2ab2c8a9ef0a78b1fa5bf27",
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  },
  "key_cert": {
    "not_after": "2027-09-13T16:32:17Z",
    "not_before": "2026-09-13T16:32:17Z",
    "root_key_id": "251b14346af43d1d",
    "root_public_key": "-----BEGIN PUBLIC KEY-----\nMCowBQYDK2VwAyEA/jJuYipI/y6/GDbKYKO/opSFVu3yu0MjlTQ9qtZrKjg=\n-----END PUBLIC KEY-----\n",
    "schema": "turiya/key-cert/1",
    "signature": "a93f8a31060bdcf2e92fa8667ac11e3d3e3d9801c1f5928adb7bce6e6f787dc029a804703bce025347424fce6067008172bdaf17cd6d04f82ba644c98642f900",
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  }
}