Casey Murphy
在使用最廣泛的技術指標中，移動平均數被用來判斷當前趨勢的方向。每一種移動平均數（本文中將簡寫成MA）都是過去數據平均計算的數學結果。一旦確定，平均結果將會被繪制到一個圖表中，使交易員能夠觀察平滑數據而不是把註意力集中在所有的金融市場每天的價格波動上。
最簡單的移動平均數被稱為數學簡單移動平均線，通過算數均數對給定數值進行計算。例如，要計算基本的10天移動平均數，你需要把過去10天的收盤價格加在一起然後除以10。在下圖中，過去10天的總價（110）除以天數（10）取得10天移動平均數。如果交易員想查看過去50天的移動平均數，計算方法相同，但是要統計過去50天的價格。下面價格的平均結果將會被考慮進過去10天的數據點以便使交易員了解一個資產在過去10天是如何定價的。
你或許會疑惑為什麼技術交易員把這一工具稱為“移動平均數”？答案是隨著新數據點的出現，老的數據點必須被新數據點取代。因此，數據隨著新數據點的出現不斷移動的。這種方式保證計算的是最新數據。在下圖中，一旦新數據點5出現，紅色的方格（過去10個數據點）向右移動並且最左邊的數據點15將會被在計算中剔除。因為相對小的數值5代替了相對大的數值15，我們將發現移動平均數的減小，從11變成10.
移動平均數是什麼樣的？
一旦一個移動平均數的數值被計算出來，他們將會被添加到一個圖表中之後連接起來組成移動平均線。這些曲線在技術交易員的圖表中很常見，但是他們的用法卻有很大區別。正如你在下圖中看到的，可以通過調整時間週期在圖表中加入不止一條移動平均線。這些曲線在開始時可能會分散並使人困惑，但是隨著時間的推移你會逐漸適應他們。下圖中的紅線是50天移動平均數，藍線是100天移動平均數。
現在你知道了什麼是移動平局線和它的樣子，下面將介紹幾種不同的移動平均線類型。
簡單移動平均線非常受交易員的歡迎，但是像所有的技術指標一樣，它也有批評者。許多人認為移動平均線的作用有限，因為每一個點的數據加權是相同的，沒有順序之分。批評者認為最近數據比過去數據更加重要應該對最後結果有更大的影響。為了回應這些批評，交易員開始給最近的數據更大的加權，這導致了各種新的移動平均線的產生，其中最受歡迎的是指數移動平均線。
指數移動平均線
指數移動平均線是一種給最近價格更多加權並使其更能應對最新信息的移動平均線。學習這個複雜的指數移動平均線計算公式對交易員來說可能是不必要的，因為幾乎所有的圖表都會為你做出計算。但是如果你是數學怪才，指數移動平均數的計算方程如下：
當使用這個方程式計算指數移動平均數值的第一個點時，你可能會註意到會之前的指數移動平均線的數值可用。這個問題可以通過計算簡單移動平均線開始。
指數移動平均線和簡單移動平均線的區別
現在你已經更好的了解了指數移動平均線和簡單移動平均線是怎樣計算的，讓我們來看一下他們的區別。通過觀察指數移動平均線的計算，你會發現它更加強調最近的數據點，使其成為一種加權平均。在下圖中，使用的時間週期是相同的（15），但是指數移動平均數反映價格變化更加迅速。註意當價格升高時指數移動平均數有一個更高值，而價格下降時其下降比簡單一定平均數更快。這是交易員相對於簡單移動平均數更加傾向使用指數移動平均數的原因。
不同的天數意味著什麼？
移動平均線是一個完全可定制指標，這就意味著使用者可以自由選擇時間框架創建移動平均數。最常用的時間週期是15、20、30、50、100和200天。創建移動平均線的時間跨度越小，對當前價格變化越敏感。隨著時間跨度的增加敏感度會減弱，或者更平滑。在你使用移動平均線的時候沒有“正確”的時間框架。找出最適合你的時間框架的方式是嘗試多個時間框架直到找到適合你交易策略的那個。
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.
本文返佣由兄弟財經提供
文章來源：http://www.investopedia.com/university/movingaverage/movingaverages1.asp