动向指数(DMI)

1． 指标说明
    动向指数又叫移动方向指数或趋向指数。是属于趋势判断的技术性指标，其基本原理是通过分析股票价格在上升及下跌过程中供需关系的均衡点，即供需关系受价格变动之影响而发生由均衡到失衡的循环过程，从而提供对趋势判断的依据。
动向的指数有三条线：上升指标线，下降指标线和平均动向指数线。三条线均可设定天数，一般为１４天。

2． 运用原则
    动向指数在应用时，主要是分析上升指标＋ＤＩ，下降指标－ＤＩ和平均动向指数ＡＤＸ三条曲线的关系，其中＋ＤＩ和－ＤＩ两条曲线的走势关系是判断出入市的讯号，ＡＤＸ则是对行情趋的判断讯号。

• 升指标＋ＤＩ和下降指标－ＤＩ的应用法则
  ①走势在有创新高的价格时，＋ＤＩ上升，－ＤＩ下降。因此，当图形上＋ＤＴ１４从下向上递增突破－ＤＴ１４时，显示市场内部有新的多头买家进场，愿意以较高的价格买进，因此为买进讯号。
  ②相反，当－ＤＩ１４从下向上递增突破＋ＤＩ１４时，显示市场内部有新的空头卖家出货，愿意以较低价格沽售，因此为卖出讯号。
  ③当走势维持某种趋势时，＋ＤＩ１４和－ＤＩ１４的交叉突破讯号相当准确，但走势出现牛皮盘档时，应＋ＤＩ１４和－ＤＩ１４发出的买卖讯号视为无效。

• 平均动向指标ＡＤＸ的应用法则
  ①趋势判断。当行情走势朝向单一方向发展时，无论是涨势或跌势，ＡＤＸ值都会不断递增。因此，当ＡＤＸ值高于上日时，可以断定当前市场行情仍在维持原有趋势，即股价会继续上涨，或继续下跌。特别是当＋ＤＩ１４与ＡＤＸ同向上升，或－ＤＩ与ＡＤＸ同向上升时，表示当前趋势十分强劲。
  ②牛皮市判断。当走势呈牛皮状态，股价新高及新低频繁出现，＋ＤＩ和－ＤＩ愈走愈近，反复交叉，ＡＤＸ将会出现递减。当ＡＤＸ值降低至２０以下，且出现横向移动时，可以断定市场为牛皮市。此时趋势无一定动向，投资者应持观望，不可认为±ＤＩ１４发出的讯号入市。
  ③转势判断。当ＡＤＸ值从上涨高点转跌时，显示原有趋势即将反转，如当前处于涨势，表示跌势临近，如当前处于跌势，则表示涨势临近。此时±ＤＩ有逐渐靠拢或交叉之表现。ＡＤＸ在高点反转斩数值无一定标准，一般以高度在５０以上转跌较为有效。观察时，ＡＤＸ调头向下，即为大势到顶或到底之讯号。当走势维持某种趋势时，＋ＤＩ１４和－ＤＩ１４的交叉突破讯号相当准确，但走势出现牛皮盘档时，应将＋ＤＩ１Ｌ４和－ＤＩ１４发出的买卖讯号视为无效。
  

• 不需要主观判断，只需要在有效市场讯号下采取行动。而且上升指标与下降指标的交错讯号容易理解。

• 在动向指数中增添ＡＤＸＲ指标，能够扩充动向的指数的功能。ＡＤＸＲ是ＡＤＸ的“评估数值”，其计算方法是将当日的ＡＤＸ值与１４日前斩ＡＤＸ值相加后除以２得出。ＡＤＸＲ的波动一般较ＡＤＸ平缓，当±ＤＩ相交，发出买卖讯号后，ＡＤＸＲ又与ＡＤＸ相交，则是最后的出入市机会，随后而来的行情较急，因此应立即采取行动。
  ＡＤＸＲ还是市场的评估指标，当ＡＤＸＲ处于高位时，显示行情波动较大，当ＡＤＸＲ处一低档，则表明行情较为牛皮。

• 计算复杂，公式不易掌握。

• ADX: The Trend Strength Indicator

  by Candy Schaap (Contact Author | Biography) Filed Under: Active Trading, Forex, Futures Trading in the direction of a strong trend reduces risk and increases profit potential. The average directional index (ADX) is used to determine when price is trending strongly. In many cases, it is the ultimate trend indicator. After all, the trend may be your friend, but it sure helps to know who your friends are. In this article in this article, we'll examine the value of ADX as a trend strength indicator.
  
  Introduction to ADX
  ADX is used to quantify trend strength. ADX calculations are based on a moving average of price range expansion over a given period of time. The default setting is 14 bars, although other time periods can be used. ADX can be used on any  trading vehicle such as stocks, mutual funds, exchange-traded funds and futures. (For background reading, see Exploring Oscillators and Indicators: Average Directional Index and Discerning Movement With The Average Directional Index - ADX.)
  
  ADX is plotted as a single line with values ranging from a low of zero to a high of 100. ADX is non-directional; it registers trend strength whether price is trending up or down. The indicator is usually plotted in the same window as the two directional movement indicator (DMI) lines, from which ADX is derived (Figure 1).
  
  For the remainder of this article, ADX will be shown separately on the charts for educational purposes.
   
  Source: TDAmeritrade Strategy Desk Figure 1: ADX is nondirectional and quantifies trend strength by rising in both uptrends and downtrends.
  When the +DMI is above the -DMI, prices are moving up, and ADX measures the strength of the uptrend. When the -DMI is above the +DMI, prices are moving down, and ADX measures the strength of the downtrend.
  
  Figure 1 is an example of an uptrend reversing to a downtrend. Notice how ADX rose during the uptrend, when +DMI was above -DMI. When price reversed, the -DMI crossed above the +DMI, and ADX rose again to measure the strength of the uptrend.
  
  Quantifying Trend Strength
  ADX values help traders to identify the strongest and most profitable trends to trade. The values are also important for distinguishing between trending and non-trending conditions.
  
  Many traders will use ADX readings above 25 to suggest that the trend's strength is strong enough for trend trading strategies.Conversely, when ADX is below 25, many will avoid trend trading strategies.
   
  ADX Value Trend Strength 0-25 Absent or Weak Trend 25-50 Strong Trend 50-75 Very Strong Trend 75-100 Extremely Strong Trend Figure 2: ADX Values and Trend Strength
  Low ADX is a usually a sign of accumulation or distribution. When ADX is below 25 for more than 30 bars, price enters range conditions and price patterns are often easier to identify. Price then moves up and down between resistance and support to find selling and buying interest, respectively. From low ADX conditions, price will eventually break out into a trend. In Figure 3, price moves from a low ADX price channel to an uptrend with strong ADX.
  
  Source: TDAmeritrade Strategy Desk Figure 3: When ADX is below 25, price enters a range. When ADX rises above 25, price tends to trend.   Source: TDAmeritrade Strategy Desk Figure 4: Periods of low ADX lead to price patterns. This chart shows a cup and handle formation that starts an uptrend when ADX rises above 25.
  The direction of the ADX line is important for reading trend strength. When the ADX line is rising, trend strength is increasing and price moves in the direction of the trend. When the line is falling, trend strength is decreasing, and price enters a period of retracement or consolidation. (For more on this topic, check out Retracement Or Reversal: Know The Difference.)
  
  A common misperception is that a falling ADX line means the trend is reversing. A falling ADX line only means the trend strength is weakening, but it usually does not mean the trend is reversing unless there has been a price climax. As long as ADX is above 25, it is best to think of a falling ADX line as simply less strong (Figure 5).
    Source: TDAmeritrade Strategy Desk Figure 5: When ADX is below 25, the trend is weak. When ADX is above 25 and rising, the trend is strong. When ADX is above 25 and falling, the trend is less strong.
  Trend Momentum
  The series of ADX peaks are also a visual representation of overall trend momentum. ADX clearly indicates when the trend is gaining or losing momentum. Momentum is the velocity of price. A series of higher ADX peaks means trend momentum is increasing. A series of lower ADX peaks means trend momentum is decreasing.
  
  Any ADX peak above 25 is considered strong, even if it is a lower peak. In an uptrend, price can still rise on decreasing ADX momentum because overhead supply is eaten up as the trend progresses (Figure 6).
  
  Knowing when trend momentum is increasing gives the trader confidence to let profits run instead of exiting before the trend has ended. However, a series of lower ADX peaks is a warning to watch price and manage risk. The best trading decisions are made on objective signals, not emotion.
  
  Source: TDAmeritrade Strategy Desk Figure 6: ADX peaks are above 25 but getting smaller. The trend is losing momentum but the uptrend remains intact.
  ADX can also show momentum divergence. When price makes a higher high and ADX makes a lower high, there is negative divergence, or nonconfirmation. In general, divergence is not a signal for a reversal, but rather a warning that trend momentum is changing. It may be appropriate to tighten the stop-loss or take partial profits. (For related reading, check out Divergences, Momentum And Rate Of Change.)
  
  Any time the trend changes character, it is time to assess and/or manage risk. Divergence can lead to trend continuation, consolidation, correction or reversal (Figure 7).
  
  Source: TDAmeritrade Strategy Desk Figure 7: Price makes a higher high while ADX makes a lower high. In this case, the negative divergence lead to a trend reversal.
  Strategic Use of ADX
  Price is the single most important signal on a chart. Read price first, and then read ADX in the context of what price is doing. When any indicator is used, it should add something that price alone cannot easily tell us. For example, the best trends rise out of periods of price range consolidation. Breakouts from a range occur when there is a disagreement between the buyers and sellers on price, which tips the balance of supply and demand. Whether it is more supply than demand, or more demand than supply, it is the difference that creates price momentum.
  
  Breakouts are not hard to spot, but they often fail to progress or end up being a trap. But ADX tells you when breakouts are valid by showing when ADX is strong enough for price to trend after the breakout. When ADX rises from below 25 to above 25, price is strong enough to continue in the direction of the breakout.
  
  Conversely, it is often hard to see when price moves from trend to range conditions. ADX shows when the trend has weakened and is entering a period of range consolidation. Range conditions exist when ADX drops from above 25 to below 25. In a range, the trend is sideways and there is general price agreement between the buyers and sellers. ADX will meander sideways under 25 until the balance of supply and demand changes again. (For more see, Trading Trend Or Range?)
  
  ADX gives great strategy signals when combined with price. First, use ADX to determine whether prices are trending or non-trending, and then choose the appropriate trading strategy for the condition. In trending conditions, entries are made on pullbacks and taken in the direction of the trend. In range conditions, trend trading strategies are not appropriate. However, trades can be made on reversals at support (long) and resistance (short).
  
  Conclusion: Finding Friendly Trends
  The best profits come from trading the strongest trends and avoiding range conditions. ADX not only identifies trending conditions, it helps the trader find the strongest trends to trade. The ability to quantify trend strength is a major edge for traders.
  
  ADX also identifies range conditions, so a trader won't get stuck trying to trend trade in sideways price action. In addition, it shows when price has broken out of a range with sufficient strength to use trend trading strategies. ADX also alerts the trader to changes in trend momentum, so risk management can be addressed. If you want the trend to be your friend, you'd better not let ADX become a stranger. The average directional index (ADX) is a trend indicator used to measure the strength and momentum of an existing trend. This indicator's main focus is not on the direction of the trend but with the momentum.
  
  The ADX is a combination of two price movement measure, the positive directional indicator (+DI) and the negative directional indicator (-DI). The +DI measures the strength of the upward trend while the –DI measures the strength of the downward trend. These two measures are also plotted along with the ADX line.
  
  Calculation
  The calculation for the ADX is considerably complex and entails several calculations that go beyond the scope of this tutorial. But, below is the general formulation of the index.
  
  
  The ADX along with the +DI and –DI are plotted between a bounded range of zero and 100. The standard time period used in this indicator is 14 periods.
  
  Because the ADX is a range-bounded indicator, it gives certain signals when the indicator moves to new levels.
  
  When the ADX is above 40 the trend is considered to have a lot of directional strength either up or down depending on the current direction of the trend. Extreme readings to the upside are considered to be quite rare compared to low readings. When the ADX indicator is below 20 the trend is considered to be weak or non-trending.
  
  The strength in a trend is considered to weaken or strengthen when these lines (40 and 20) are crossed by the ADX. When the ADX has had a strong move above 40 but fails to remain above, it is suggested that the trend is weakening and will reverse. When the ADX moves above 20 it is a sign that a new trend in the security is starting.
  
  
  It is important to remember that in regard to this trend indicator the ADX does not care about the direction of the trend it only is concerned with the strength of it. When the ADX is high there is strength in a trend. When it is low it signals little to no trending in the security. When there are shifts in the ADX it is a signal of a new trend or trend reversal.
  
  The two measures used to compute the ADX are also used to signal weakening in trends and the starting of new trends. Signals are formed when the two lines, the +D and –D, crossover each other. A buy signal is formed when the +D, which measures the upward trend, crosses above the –D, which measures the downward trend. A sell signal is formed when the –D crosses above the +D. These crossovers signal a shift from an upward trend to a downward trend or visa versa.
  
  This trend indicator is extremely popular and useful as it combines both aspects of trend strength with the ADX and the direction of trends with the +DI/-DI lines. Is another useful indicator for any technical trader.
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