# ADR-017: Multi-Algorithm Consensus Over Single Discovery

| Field     | Value                                    |
|-----------|------------------------------------------|
| Status    | Accepted                                 |
| Type      | 1 — Architectural                        |
| Score     | 0.85                                     |
| Date      | 2026-02-18                               |
| Decider   | Conductor                                |

## Context

No single causal discovery algorithm dominates across all data settings.
The PC algorithm excels when the faithfulness assumption holds and sample
sizes are moderate. GES excels with finite samples and makes stronger
parametric assumptions. Running both and taking consensus reduces false
positives from either method's assumptions.

## Decision

Include a causal edge only if at least 2 out of 3 discovery methods agree
(threshold ≥ 0.66). Each consensus edge records which algorithms support it,
providing full provenance for regulatory review.

## Consequences

- **Reduced false discovery rate**: edges must pass multiple independent tests.
- **Full provenance**: every edge traces back to supporting algorithms.
- **Computational cost**: 2-3x single algorithm (acceptable for batch discovery).
- **Extensible**: add a third algorithm (e.g., FCI) without changing consensus API.
