# ADR-006 — No composite score in Phase 1

Status: accepted (2026-09-08)

## Context

A single "impact" or "priority" score per cancer is attractive for headlines and for the homepage,
and the specification foresees composite indexes (CI-IMPACT etc.) in a later phase (§353). Composite
scores, however, hide weighting choices, mix units and uncertainty levels, and are the values most
likely to be misread as clinical or policy verdicts. In Phase 1 the platform still lacks the burden
layer for most of the world (GLOBOCAN license review, SEER credentials), so any composite would be
dominated by whichever inputs happen to exist.

## Decision

Phase 1 ships **single-input, fully explained metrics only** — the catalog in
`packages/database/src/seed-data/metrics.ts` (burden counts and rates, mortality-to-incidence ratio,
5-year survival, trial counts, publication counts and growth, curated evidence and gene counts,
genomic cohorts) plus two **two-input gap indexes** (`trial_gap`, `research_gap`) whose formula is a
transparent percentile difference within one scope. No weighted sum across metrics is computed,
stored or displayed. The `rankings.breakdown` column and the `composite` category in
`metric_definitions` exist in the schema but remain unused.

## Consequences

- Every ranking on the site answers a precise question ("which cancers have the most recruiting
  trials?"), with scope, year, source and formula version visible and "Why this rank?" available.
- The homepage cannot present a single master ordering; it presents several rankings side by side
  with their scopes, and the methodology page states explicitly that composites are not computed yet.
- When a composite is introduced (Phase 2+), it must: publish weights and components in
  `rankings.breakdown`; be versioned like any formula; be computed only where all components exist
  in the same scope (no imputation); be marked `experimental` until reviewed; and never be labelled
  as a measure of importance of a disease or a judgement on research communities (spec §324).