ADVANCE/DECLINE RATIO

Overview
The Advance/Decline Ratio ("A/D Ratio") shows the ratio of advancing issues to declining issues. It is calculated by dividing the number of advancing issues by the number of declining issues.

Interpretation
The A/D Ratio is similar to the Advancing-Declining Issues in that it displays market breadth. But, where the Advancing-Declining Issues subtracts the advancing/declining values, the A/D Ratio divides the values. The advantage of the Ratio is that it remains constant regardless of the number of issues that are traded on the New York Stock Exchange (which has steadily increased).
A moving average of the A/D Ratio is often used as an overbought/oversold indicator. The higher the value, the more "excessive" the rally and the more likely a correction. Likewise, low readings imply an oversold market and suggest a technical rally.
Keep in mind, however, that markets that appear to be extremely overbought or oversold may stay that way for some time. When investing using overbought and oversold indicators, it is wise to wait for the prices to confirm your belief that a change is due before placing your trades.
Day-to-day fluctuations of the Advance/Decline Ratio are often eliminated by smoothing the ratio with a moving average.

Example
The following chart shows the S&P 500 and a 15-day moving average of the A/D Ratio.



You can see that prices usually declined after entering the overbought level above 1.25 ("sell" arrows) and that they usually rallied after entering the oversold level below 0.90 ("buy" arrows).

Calculation
The A/D Ratio is calculated by dividing the number of stocks that advanced in price for the day by the number of stocks that declined.



Table 3 shows the calculation of the A/D Ratio.

ADVANCE/DECLINE LINE

Overview
The Advance/Decline Line ("A/D Line") is undoubtedly the most widely used measure of market breadth. It is a cumulative total of the Advancing-Declining Issues indicator. When compared to the movement of a market index (e.g., Dow Jones Industrials, S&P 500, etc) the A/D Line has proven to be an effective gauge of the stock market's strength.

Interpretation
The A/D Line is helpful when measuring overall market strength. When more stocks are advancing than declining, the A/D Line moves up (and vice versa).
Many investors feel that the A/D Line shows market strength better than more commonly used indices such as the Dow Jones Industrial Average ("DJIA") or the S&P 500 Index. By studying the trend of the A/D Line you can see if the market is in a rising or falling trend, if the trend is still intact, and how long the current trend has prevailed.
Another way to use the A/D Line is to look for a divergence between the DJIA (or a similar index) and the A/D Line. Often, an end to a bull market can be forecast when the A/D Line begins to round over while the DJIA is still trying to make new highs. Historically, when a divergence develops between the DJIA and the A/D Line, the DJIA has corrected and gone the direction of the A/D Line.
A military analogy is often used when discussing the relationship between the A/D Line and the DJIA. The analogy is that trouble looms when the generals lead (e.g., the DJIA is making new highs) and the troops refuse to follow (e.g., the A/D Line fails to make new highs).

Example
The following chart shows the DJIA and the A/D Line.



The DJIA was making new highs during the 12 months leading up to the 1987 crash. During this same period, the A/D Line was failing to reach new highs. This type of divergence, where the generals lead and the troops refuse to follow, usually results in the generals retreating in defeat as happened in 1987.
Calculation




Because the A/D Line always starts at zero, the numeric value of the A/D Line is of little importance. What is important is the slope and pattern of the A/D Line.