OpenChainGraph Suite · OCG v0.8.0 · Fair Lending & Adverse Action · Cluster ㉖

Fair Lending Disparity Audit

Note (dated 2026-08-04): a chain composes independent computations performed in an analytical order. No step's output is carried into the next step by the execution model; each step computes from its own declared inputs. This is true of every chain on this site, including chains whose per-step copy below reads as a data handoff.

Gated two-step chain for fair lending disparity analysis. Step 1 computes HMDA rate-spread reportability using the FFIEC APOR methodology (1.5 pp and 3.5 pp thresholds) to establish context for the audit population. Step 2 computes disparity metrics from aggregate counts: the 4/5ths (80%) adverse-impact ratio, two-proportion z-statistic, odds ratio, and standardized mean difference. A §21.4 gate exits with remediation required when AIR falls below 0.8; the default path completes as a clean audit pass. All computation operates on aggregate counts only — zero PII by construction.

OpenChainGraph · 2 Steps compliance mandate · §21.4 Gate Hash-Anchored §4 chain_depth:2 Zero PII · Aggregate Only
Not legal or compliance advice. The 4/5ths rule and statistical tests are screening tools; a single adverse-impact ratio does not establish or negate a fair lending violation. Consult counsel for ECOA, FHA, and HMDA analysis.
🔒 ZERO PII BY CONSTRUCTION. Both nodes in this chain accept aggregate counts only. No individual applicant records, names, or demographic identifiers are processed at any stage. All computation runs locally in your browser. No data is transmitted.
⚡ §21.4 Decision Gate active at Step 2: chain exits requiring remediation when adverse_impact_ratio < 0.8 (4/5ths rule fail). When AIR ≥ 0.8, the chain completes as a disparity audit pass.
Chain Topology (§21.4 gated) — HMDA Rate Spread → Disparity Metrics [GATE]
§4 Execution Hash · Chain Definition Anchor
execution_hash:computing…
Chain Stages · 2 Steps · 1 Decision Gate (§21.4)
1 ROOT node
HMDA Rate Spread art-230-compute-hmda-rate-spread
HMDA rate-spread reportability screen using FFIEC APOR methodology. First-lien threshold 1.5 pp; subordinate-lien threshold 3.5 pp; HELOC first-lien 6.5 pp. Establishes whether the loan population warrants HMDA reporting context for the disparity audit in Step 2.
MCP Call · compute_hmda_rate_spread
{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "compute_hmda_rate_spread",
    "arguments": {
      "loan_apr_pct": 7.2,
      "apor_pct": 6.1,
      "lien_type": "first_lien",
      "product_type": "fixed",
      "rate_lock_date": "2026-07-04"
    }
  },
  "id": 1
}
https://mcp.ainumbers.co/mcp
↓
2 GATE & TERMINAL node §21.4 gate
Disparity Metrics art-229-compute-disparity-metrics
Computes adverse-impact ratio (4/5ths rule per 29 CFR §1607.4(D)), two-proportion z-statistic (one-tail and two-tail), odds ratio, and standardized mean difference from aggregate group counts. Gate: adverse_impact_ratio < 0.8 exits requiring remediation. Default (AIR ≥ 0.8) completes the audit as a pass. Aggregate counts only — zero PII.
△ Gate: if /adverse_impact_ratio < 0.8 → END (remediation required)  |  default → END (pass)
MCP Call · compute_disparity_metrics
{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "compute_disparity_metrics",
    "arguments": {
      "reference_group_label": "White Non-Hispanic",
      "comparison_group_label": "Black or African American",
      "reference_approved": 90,
      "reference_total": 100,
      "comparison_approved": 70,
      "comparison_total": 100
    }
  },
  "id": 2
}
https://mcp.ainumbers.co/mcp
Export Chain Artifact
Download a §4-compliant chain artifact with execution hash, step definitions, and gate configuration. Hash is deterministic over canonical {policy_parameters, output_payload} per RFC 8785/JCS.

Ask your agent

Copy this paragraph into Claude, OpenClaw, or any MCP-aware agent to run this whole workflow on the server and check one field that answers a real question.

Question: Before this file goes to the examiner, does the priced loan cross the HMDA rate-spread reporting line?
Run the AINumbers MCP tool `run_chain` with {"chain":"fair-lending-disparity-audit"} and read `art-230-compute-hmda-rate-spread.is_reportable`.
Re-run with `inputs` for `art-230-compute-hmda-rate-spread`, reusing the values that result echoed, with `apr_pct` set to 1. Compare the same field.
Verify: call `verify_execution_hash` (https://mcp.ainumbers.co/mcp) with `claimed_hash` set to `composite_execution_hash` and the full `composite_artifact`.
Ledger, for a human re-check: https://ledger.ainumbers.co/
PII rule: send synthetic or anonymised inputs only. The MCP server runs these kernels and logs no payloads.
Chain page: https://ainumbers.co/chaingraph/chains/fair-lending-disparity-audit.html