Breadth

A technical analysis metric that measures the degree of participation in a market move by counting the number of advancing versus declining stocks.

Market breadth is a technical analysis concept that measures the degree of participation in a market move by counting the number of individual stocks advancing versus those declining. It helps investors determine whether an index's upward or downward movement is being driven by a healthy, broad-based consensus of many companies or by just a few heavily weighted mega-cap stocks. To observe breadth, analysts look at indicators such as the Advance-Decline Line (A/D Line), the percentage of stocks trading above their 50-day or 200-day moving averages, or the ratio of up-volume to down-volume. These metrics reveal the underlying strength of a market trend beneath the surface of capitalization-weighted indices. For retail investors, weak breadth during a market rally is a major warning sign. If a major index is rising but more individual stocks are falling than rising, the rally is fragile and highly vulnerable to a reversal if those few leading mega-caps stumble. Conversely, strong breadth indicates a robust, sustainable market trend with wide participation across sectors.

On a given trading day, the S&P 500 index rises by 1.2%. However, an analysis of the underlying stocks shows that 150 companies closed higher (advancing issues) while 350 companies closed lower (declining issues). The net market breadth for the day is 150 - 350 = -200, indicating poor breadth despite the index's positive return.