A form of technical analysis that examines the range between high and low stock prices over a period of time. The Mass Index, developed by Donald Dorsey in the early 1990s, suggests that a reversal of the current trend will likely take place when the range widens beyond a certain point and then contracts.
To determine the Mass Index, first calculate the nine-day exponential moving average (EMA) of the range between the high and low prices for a period of time – typically 25 days. Then divide this figure by the nine-day exponential moving average of the moving average in the numerator. The equation looks like this:
Dorsey hypothesized that, when the figure jumps above 27 – creating a “bulge” – and then drops below 26.5, the stock is ready to change course. An index of 27 represents a rather volatile stock, so some traders set a lower baseline when determining the presence of a price bulge.