ADX - Average Directional Movement Index

ADX - Average Directional Movement Index Technical Indicator helps to determine if there is a price trend. ADX was developed and described in detail by Welles Wilder in his book "New Concepts in Technical Trading Systems".

ADX is an oscillator that fluctuates between 0 and 100. Even though the scale is from 0 to 100, readings above 60 are relatively rare. Low readings, below 20, indicate a weak trend and high readings, above 40, indicate a strong trend. The indicator does not grade the trend as bullish or bearish, but merely assesses the strength of the current trend. A reading above 40 can indicate a strong downtrend as well as a strong uptrend.

The simplest trading method based on the system of directional movement implies comparison of two direction indicators: the 14-period +DI one and the 14-period -DI. To do this, one either puts the charts of indicators one on top of the other, or +DI is subtracted from -DI. W. Wilder recommends buying when +DI is higher than -DI, and selling when +DI sinks lower than -DI.

In its most basic form, buy and sell signals can be generated by +DI/-DI crosses. A buy signal occurs when +DI moves above -DI and a sell signal when -DI moves above the +DI. Be careful, though; when a security is in a trading range, this system may produce many whipsaws. As with most technical indicators, +DI/-DI crosses should be used in conjunction with other aspects of technical analysis.

ADX combines +DI with -DI and then smoothes the data with a moving average to provide a measurement of trend strength. Because it uses both +DI and -DI, ADX does not offer any indication of trend direction, just strength. Generally, readings above 40 indicate a strong trend and readings below 20 a weak trend. To catch a trend in its early stages, you might look for stocks with ADX that advances above 20. Conversely, an ADX decline from above 40 might signal that the current trend is weakening and a trading range may develop.

More on ADX can be found in Wilder's book, New Concepts in Technical Trading Systems, written in 1978. Wilder's indicators remain some of the best and most popular indicators today.