When the index rises but fewer stocks join
A practical way to read advance–decline divergence before you treat a headline rally as permission to add risk in the same places.
Portfolio meetings often open with the index level. That number is useful and incomplete. When fewer constituents participate in an advance, sector and stock-level risk can be concentrating even as the headline looks calm.
What to look at first
Start with a simple advance–decline picture for the market you actually trade — not a global proxy you do not hold. Pair it with new highs versus new lows over the same window. If the index is making progress while the advance–decline line stalls, treat that as a prompt to inspect which sectors still have wide participation.
What it does not mean
Narrow breadth is not an automatic sell signal. It can persist longer than discomfort allows. The useful question for a sector rotation briefing is whether your overweight industries are among the narrowing leaders or among the neglected names quietly improving.
How we use it in briefings
In a Market Breadth Assessment we score the recent window, then cross-check against the sector map so the conversation stays tied to allocation weights rather than to a single chart anecdote.