evidence

Record one supporting or refuting observation against a belief. Mneva runs sequential probability ratio testing (SPRT) on the accumulated evidence — when the log-likelihood crosses the promote or demote threshold, confidence shifts and sprt_status flips.

This is how a belief earns its place over time. See Evidence (SPRT) for the math behind the thresholds.

Signature

evidence({
  belief_id: number,
  kind: 'supporting' | 'refuting',
  strength: number,           // 0.1..0.9 (clamped)
  note?: string
}) → {
  evidence_id: number,
  belief_id: number,
  kind: string,
  strength: number,
  log_likelihood: number,
  new_log_ratio: number,
  new_confidence: number,
  confidence_delta: number,
  status: 'accumulating' | 'promoted' | 'demoted',
  boundaries: { promote: number, demote: number }
}

Example

Belief #1 is "the worker pool should be sized at 4 threads", confidence 0.6.

curl -X POST https://mneva.dev/v1/evidence \
  -H "x-mneva-key: $MNEVA_KEY" \
  -H "content-type: application/json" \
  -d '{
    "belief_id": 1,
    "kind": "refuting",
    "strength": 0.85,
    "note": "production needed 8 threads under load"
  }'

Response:

{
  "evidence_id": 2,
  "belief_id": 1,
  "kind": "refuting",
  "strength": 0.85,
  "log_likelihood": -1.7346,
  "new_log_ratio": -3.4692,
  "new_confidence": 0.4,
  "confidence_delta": -0.2,
  "status": "demoted",
  "boundaries": { "promote": 2.89, "demote": -2.25 }
}

This was the second refuting observation at strength 0.85. Each contributed ln(0.15/0.85) ≈ -1.735. Cumulative ratio is now -3.47, past the demote boundary (-2.25). Status flipped to demoted, confidence dropped by 0.20 (down to 0.40).

What the response means

• log_likelihood — the contribution this evidence added to the SPRT accumulator.
• new_log_ratio — the cumulative log ratio across all evidence on this belief.
• confidence_delta — how much confidence moved on this call (0 if no boundary was crossed, +0.10 on promote, -0.20 on demote).
• status — accumulating (still between boundaries), promoted (past +2.89), or demoted (past -2.25).

Status only flips once per direction. The second demote-crossing evidence doesn't double-penalize; the audit trail in evidence_for still records every event.

See also

• evidence_for — read the trail
• revise — what to do when a belief is demoted
• Evidence (SPRT) — concept + math