Friday 7 May 2010


Technical indicators are constructed by manipulating some aspect of price such as a moving average of prices over a 10 day period. The Relative Strength Indicator (RSI) tries to anticipate a change in the trend. This is a leading indicator of a trend change. The results are used to deliver messages about the strength of the market. It is called an oscillator because the indicator readings are converted into percentage results which range from 0% to 100%. The position of each day’s indicator reading gives the trader an indication of the strength, or weakness, of the existing price trend.
The RSI is calculated by monitoring changes in the closing prices of the stock. The number of higher closes is compared to the number of lower closes for the selected period. The RSI compares the internal strength of a stock by looking at the average of the upwards price changes and comparing it with the average of the downward price changes. The results are expressed as a percentage, providing the upper and lower boundaries. The plotted results oscillate between these two levels and give traders information about the speed and acceleration of the changes. Traders use either a 14, 9, or 7 day period in the Relative Strength Calculation.
In this sense the RSI is very similar to a stochastic and uses similar principles. Where the stochastic quantifies the ability of the market to close near the high or the low of the day, the RSI quantifies the strength of the way the market moves higher, or lower. The over-bought and over-sold signals are the same as any oscillator, although with an RSI they are traditionally set at 70% and 30%.
The most significant trading signal delivered by any oscillator style indicator is a divergence signal. This sounds complicated but it just means that the significant valley patterns shown by the RSI trend in the opposite direction to the significant valley patterns as shown by the price line chart. A valley is created by two distinct lows that each precede a rally from a downtrend. This builds a valley in the price chart. The lows of these valleys are joined with a short trend line as shown.
The corresponding lows on the RSI indicator are also joined by a short trend line. When the RSI line slopes differently from the price chart line, a divergence occurs. When these valleys form below the 30% area on the RSI, or form peaks above the 70% level, they are most reliable. Oscillator activity between these levels is not used to find divergence signals. Divergence signals give the trader an advantage by confirming an entry into a downtrend as it weakens and just before it turns into an up trend. It is also used to get out of an up trend as it weakens, and before it collapses into a downtrend. The divergence signal does not occur every time a trend changes, but when it does, it delivers a strong confirmation signal that a trend break is likely.
RSI divergence signals often appear in advance of a trend change, but they are not very good at suggesting the time of a trend change. The divergence signal may appear just as the trend changes, as in the chart extract, or several weeks before. Traders use the RSI divergence as an early warning signal to enable them to prepare for a trend change.
When the RSI and price chart lines move in the same way we get a confirming signal that the existing price trend is unlikely to change. These signals are not very important because we can get the same information from just looking at the chart.
The RSI is one of the very few oscillator style indicators where trend lines and support and resistance lines can be effectively used. These are used as signals to confirm the trend shown on the price chart. When other chart patterns suggest action, then the RSI trend line might also confirm this. When the RSI is used like this it does not give the trader any distinct advantage.

By Daryl Guppy