Moving Averages（6）：Different Flavors

By Casey Murphy, Senior Analyst

Most of the methods in which moving averages are used in trading have been addressed within this tutorial, but this tool has also been used in the development of other indicators. In this section, we will give you a basic introduction to a couple of these indicators, but most will require further study if you want to incorporate them into your strategy. 

Moving Average Convergence Divergence (MACD) 
One of the most popular technical indicators, the moving average convergence divergence (MACD) is used by traders to monitor the relationship between two moving averages. It is generally calculated by subtracting a 26-day exponential moving average from a 12-day EMA. When the MACD has a positive value, the short-term average is located above the long-term average. As mentioned earlier, this stacking order of the averages is an indication of upward momentum. A negative value occurs when the short-term average is below the long-term average - a sign that the current momentum is in the downward direction. Many traders will also watch for a move above or below the zero line because this signals the position where the two averages are equal (crossover strategy applies here). A move above zero would be used as a buy sign, while a cross below zero can be used as a sell signal. (For more on this, read Moving Average Convergence Divergence - Part 1 and Part 2.) 

MACD = EMA(12) – EMA(26)

MACD大于0，价格具有向上运行的趋势。

MACD由负变为正，是买入信号。

Signal/Trigger Line 
Moving averages aren't limited to just stock prices; MAs can be created for any form of data that changes frequently. It is even possible to take a moving average of a technical indicator such as the MACD. For example, a nine-period EMA of the MACD values is added to the chart in Figure 1 in an attempt to form transaction signals. As you can see, buy signals are generated when the value of the indicator crosses above the signal line (dotted line), while short signals are generated from a cross below the signal line. It is important to note that regardless of the indicator being used, a move beyond a signal line is interpreted in the same manner; the only thing that varies is the number of time periods used to create it. 

Figure 1

对MACD信号也可以做EMA(N)的运算。

实际上，很多行情软件的MACD有三个参数，

第三个参数一般就是对MACD做了EMA运算，得到了hist，

就是MACD那个红色和绿色的“柱子”。

Bollinger Band® 

A Bollinger Band® technical indicator looks similar to the moving average envelope, but differs in how the outer bands are created. 

布林带看上去和MA的包络很像，但其上轨和下轨的产生方式和MA的包络的构造方式不一样。

The bands of this indicator are generally placed two standard deviations away from a simple moving average. 

SMA加减2倍标准差（std），就是布林线。

In general, a move toward the upper band can often suggest that the asset is becoming overbought, while a move close to the lower band can suggest the asset is becoming oversold. 

上轨经常意味着发生了超买，下轨经常意味着超卖。

Since standard deviation is used as a statistical measure of volatility, this indicator adjusts itself to market conditions.

因为std是一个经常被用来衡量波动大小的统计量。

The tightening of the bands is often used by traders as an early indication that overall volatility may be about to increase and that a trader may want to wait for a sharp price move.

很窄的布林带通常被交易员们看作是波动可能会突然增大的一种前兆。在这种情况下，交易员可能会等待着由价格突然变化所带来的机会。

Figure 2