Casey Murphy
在使用最广泛的技术指标中，移动平均数被用来判断当前趋势的方向。每一种移动平均数（本文中将简写成MA）都是过去数据平均计算的数学结果。一旦确定，平均结果将会被绘制到一个图表中，使交易员能够观察平滑数据而不是把注意力集中在所有的金融市场每天的价格波动上。
最简单的移动平均数被称为数学简单移动平均线，通过算数均数对给定数值进行计算。例如，要计算基本的10天移动平均数，你需要把过去10天的收盘价格加在一起然后除以10。在下图中，过去10天的总价（110）除以天数（10）取得10天移动平均数。如果交易员想查看过去50天的移动平均数，计算方法相同，但是要统计过去50天的价格。下面价格的平均结果将会被考虑进过去10天的数据点以便使交易员了解一个资产在过去10天是如何定价的。
你或许会疑惑为什么技术交易员把这一工具称为“移动平均数”？答案是随着新数据点的出现，老的数据点必须被新数据点取代。因此，数据随着新数据点的出现不断移动的。这种方式保证计算的是最新数据。在下图中，一旦新数据点5出现，红色的方格（过去10个数据点）向右移动并且最左边的数据点15将会被在计算中剔除。因为相对小的数值5代替了相对大的数值15，我们将发现移动平均数的减小，从11变成10.
移动平均数是什么样的？
一旦一个移动平均数的数值被计算出来，他们将会被添加到一个图表中之后连接起来组成移动平均线。这些曲线在技术交易员的图表中很常见，但是他们的用法却有很大区别。正如你在下图中看到的，可以通过调整时间周期在图表中加入不止一条移动平均线。这些曲线在开始时可能会分散并使人困惑，但是随着时间的推移你会逐渐适应他们。下图中的红线是50天移动平均数，蓝线是100天移动平均数。
现在你知道了什么是移动平局线和它的样子，下面将介绍几种不同的移动平均线类型。
简单移动平均线非常受交易员的欢迎，但是像所有的技术指标一样，它也有批评者。许多人认为移动平均线的作用有限，因为每一个点的数据加权是相同的，没有顺序之分。批评者认为最近数据比过去数据更加重要应该对最后结果有更大的影响。为了回应这些批评，交易员开始给最近的数据更大的加权，这导致了各种新的移动平均线的产生，其中最受欢迎的是指数移动平均线。
指数移动平均线
指数移动平均线是一种给最近价格更多加权并使其更能应对最新信息的移动平均线。学习这个复杂的指数移动平均线计算公式对交易员来说可能是不必要的，因为几乎所有的图表都会为你做出计算。但是如果你是数学怪才，指数移动平均数的计算方程如下：
当使用这个方程式计算指数移动平均数值的第一个点时，你可能会注意到会之前的指数移动平均线的数值可用。这个问题可以通过计算简单移动平均线开始。
指数移动平均线和简单移动平均线的区别
现在你已经更好的了解了指数移动平均线和简单移动平均线是怎样计算的，让我们来看一下他们的区别。通过观察指数移动平均线的计算，你会发现它更加强调最近的数据点，使其成为一种加权平均。在下图中，使用的时间周期是相同的（15），但是指数移动平均数反映价格变化更加迅速。注意当价格升高时指数移动平均数有一个更高值，而价格下降时其下降比简单一定平均数更快。这是交易员相对于简单移动平均数更加倾向使用指数移动平均数的原因。
不同的天数意味着什么？
移动平均线是一个完全可定制指标，这就意味着使用者可以自由选择时间框架创建移动平均数。最常用的时间周期是15、20、30、50、100和200天。创建移动平均线的时间跨度越小，对当前价格变化越敏感。随着时间跨度的增加敏感度会减弱，或者更平滑。在你使用移动平均线的时候没有“正确”的时间框架。找出最适合你的时间框架的方式是尝试多个时间框架直到找到适合你交易策略的那个。
Moving Averages: What Are They?
By Casey Murphy, Senior Analyst ChartAdvisor.com
Among the most popular technical indicators, moving averages are used to gauge the direction of the current trend. Every type of moving average (commonly written in this tutorial as MA) is a mathematical result that is calculated by averaging a number of past data points. Once determined, the resulting average is then plotted onto a chart in order to allow traders to look at smoothed data rather than focusing on the day-to-day price fluctuations that are inherent in all financial markets.
The simplest form of a moving average, appropriately known as a simple moving average (SMA), is calculated by taking the arithmetic mean of a given set of values. For example, to calculate a basic 10-day moving average you would add up the closing prices from the past 10 days and then divide the result by 10. In Figure 1, the sum of the prices for the past 10 days (110) is divided by the number of days (10) to arrive at the 10-day average. If a trader wishes to see a 50-day average instead, the same type of calculation would be made, but it would include the prices over the past 50 days. The resulting average below (11) takes into account the past 10 data points in order to give traders an idea of how an asset is priced relative to the past 10 days.
Perhaps you're wondering why technical traders call this tool a "moving" average and not just a regular mean? The answer is that as new values become available, the oldest data points must be dropped from the set and new data points must come in to replace them. Thus, the data set is constantly "moving" to account for new data as it becomes available. This method of calculation ensures that only the current information is being accounted for. In Figure 2, once the new value of 5 is added to the set, the red box (representing the past 10 data points) moves to the right and the last value of 15 is dropped from the calculation. Because the relatively small value of 5 replaces the high value of 15, you would expect to see the average of the data set decrease, which it does, in this case from 11 to 10.
What Do Moving Averages Look Like?
Once the values of the MA have been calculated, they are plotted onto a chart and then connected to create a moving average line. These curving lines are common on the charts of technical traders, but how they are used can vary drastically (more on this later). As you can see in Figure 3, it is possible to add more than one moving average to any chart by adjusting the number of time periods used in the calculation. These curving lines may seem distracting or confusing at first, but you'll grow accustomed to them as time goes on. The red line is simply the average price over the past 50 days, while the blue line is the average price over the past 100 days.
Now that you understand what a moving average is and what it looks like, we'll introduce a different type of moving average and examine how it differs from the previously mentioned simple moving average.
The simple moving average is extremely popular among traders, but like all technical indicators, it does have its critics. Many individuals argue that the usefulness of the SMA is limited because each point in the data series is weighted the same, regardless of where it occurs in the sequence. Critics argue that the most recent data is more significant than the older data and should have a greater influence on the final result. In response to this criticism, traders started to give more weight to recent data, which has since led to the invention of various types of new averages, the most popular of which is the exponential moving average (EMA).
Exponential Moving Average
The exponential moving average is a type of moving average that gives more weight to recent prices in an attempt to make it more responsive to new information. Learning the somewhat complicated equation for calculating an EMA may be unnecessary for many traders, since nearly all charting packages do the calculations for you. However, for you math geeks out there, here is the EMA equation:
When using the formula to calculate the first point of the EMA, you may notice that there is no value available to use as the previous EMA. This small problem can be solved by starting the calculation with a simple moving average and continuing on with the above formula from there. We have provided you with a sample spreadsheet that includes real-life examples of how to calculate both a simple moving average and an exponential moving average.
The Difference Between the EMA and SMA
Now that you have a better understanding of how the SMA and the EMA are calculated, let's take a look at how these averages differ. By looking at the calculation of the EMA, you will notice that more emphasis is placed on the recent data points, making it a type of weighted average. In Figure 5, the numbers of time periods used in each average is identical (15), but the EMA responds more quickly to the changing prices. Notice how the EMA has a higher value when the price is rising, and falls faster than the SMA when the price is declining. This responsiveness is the main reason why many traders prefer to use the EMA over the SMA.
What Do the Different Days Mean?
Moving averages are a totally customizable indicator, which means that the user can freely choose whatever time frame they want when creating the average. The most common time periods used in moving averages are 15, 20, 30, 50, 100 and 200 days. The shorter the time span used to create the average, the more sensitive it will be to price changes. The longer the time span, the less sensitive, or more smoothed out, the average will be. There is no "right" time frame to use when setting up your moving averages. The best way to figure out which one works best for you is to experiment with a number of different time periods until you find one that fits your strategy.
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文章来源：http://www.investopedia.com/university/movingaverage/movingaverages1.asp