The composite is the harmonic mean of per-trait scores on a score card. It returns a single number that emphasizes the weakest trait: a low trait score pulls the composite down more than a high trait score pulls it up.
Given per-trait scores s1, s2, …, sn on a score card, the composite is:
composite = n / (1/s1 + 1/s2 + … + 1/sn)
The harmonic mean is always less than or equal to the arithmetic mean. The two means are equal only when all per-trait scores are equal; as the spread between traits widens, the harmonic mean falls further below the arithmetic mean.
The harmonic mean makes the composite sensitive to the lowest inputs. A single low trait score therefore has a larger downward effect than a high trait score has an upward effect. The composite behaves as a bottleneck summary: improving the weakest trait raises the composite more than improving an already-high trait.
The composite's confidence is the minimum per-trait confidence on the score card. A composite score inherits the reliability of its least reliable input, so a single low-confidence trait makes the whole composite low-confidence.
The composite's headroom is the maximum per-trait headroom on the score card. Because the harmonic mean is bottleneck-sensitive (§2.1), the trait with the largest headroom is the one whose improvement would move the composite most. Composite headroom therefore points at the trait to work on first.
The composite is useful as a single decision signal — comparing two pieces of content, routing content above a threshold, tracking a portfolio over time. It is not a substitute for per-trait scores when the decision requires knowing which trait is weak. Per-trait scores carry diagnostic information that the composite collapses.
The composite does not carry a tier label, a set of breaks, or a tier color. The following section is an index of what the composite intentionally does not include, with the reason in each case.