價格比率或相對強度指標與價格對比的目的相同——它比較了一只股票相對於另外一只股票（或指數）的表現。一些交易者將價格比率指標作為尋找突出表現股票的一種常用的工具。
價格比率的計算方法是：第一只股票的收盤價 / 第二只股票的收盤價。
與價格對比不同的是，價格比率是呈現在一個單獨的指標窗口。有以下三種可以選擇：
1. 調整後的價格比率：指標線總是從圖表的左側零處開始。
2. 價格比率（未調整）：簡單的表現出兩只股票收盤價之間的原始關系。
3. 相對強度與價格比率類似，不同的是，你可以截取任一時間段的價格走勢（該段走勢在相對強度窗口從零處開始顯示）。如果不指定週期的話，價格比率會默認為比較兩只股票所有的價格走勢。
相對強度指標與價格比率相比的優勢在於，你不必在每次改變圖表週期之後重新設置。如果你打算繪制出趨勢線或者添加備註，這一點很重要。
相對強度的交易信號
溫斯坦的《稱傲牛熊市的秘密》一書中，曼斯菲爾德圖表關於相對強度指標與相對強度的描述並不完全一致。它們十分的相似，並且都可以與溫斯坦的長期突破交易系統結合使用。
示例
利用相對強度以及價格比率指標對比蘋果公司股票與納斯達克100指數。
下面的兩條直線走勢是一致的：，價格比率是從零處開始，而相對強度指標的零點則是從所選起點處開始，2009年1月2日處為零。不同之處在於，你可以在相對強度指標上畫出趨勢線。
價格比率的計算公式
價格比率是通過一個股票的收盤價比率比上另一只股票的收盤價比率得出，從圖表的第一天開始。意思是，所選的時間週期不同，價格比率的起始點會相應變化，如果你變換時間週期，價格比率曲線似乎是在移動，但是形態會保持一致。
建議
浏覽價格比率的時候，設置一個或兩個時間週期作為參照標準（比如，3年-週；6個月-日）。
計算價格比率的方法可以按照下面計算IBM與DJI（道瓊斯工業指數）的價格比率的步驟。
1. 計算出第一日價格比率的反比： DJI / IBM.
2. 每日都計算出IBM / DJI 的值。
3. 第一步的值*第二步的值。
4. 第三步的值減去1，即可使價格比率起始點位於零點。
示例
註意：另外一種使起點為零的方法是計算出第二步的比值，接下來每一日的比值都減去第一步的值。這種方法的結果類似於上面例子。
價格相對強度的計算公式
1、 確定所截取數據的價格比率：所截取週期内兩只股票的收盤價比值。
2、 確認當前兩只股票的收盤價比值（股票1的收盤價/股票2的收盤價）。
3、 步驟1乘以步驟2，再減去1
相對強度指標是在所截取時間段内或默認時間内，利用一只股票的收盤價比率與另一只股票或指數的收盤價比率計算而來。默認的時間段是兩只股票上市以來的所有價格走勢數據。比如，如果我們對比微軟公司與標普500指數的價格相對強度，那麼微軟公司的起始時間是1993年6月1日，早於標普500指數的起始時間1980年1月2日。
Price Ratio (Relative Strength)
The Price Ratio (or relative strength - comparative) serves a similar purpose to Price Comparison - it compares the performance of one stock relative to another (or to an index). Some traders use the Price Ratio as a general tool to select outperforming stocks.
Price Ratio is calculated by dividing the closing price of the first stock by the second.
Unlike Price Comparison, Price Ratio is plotted in a separate indicator panel. There are three options available:
1. Price Ratio is adjusted so that the indicator line always starts at zero on the left of the chart.
2. Price Ratio (Unadjusted) makes no such adjustment and simply displays the raw ratio of closing price between two securities.
3. Relative Strength is similar to Price Ratio except that you are able to set the intercept date (at which the indicator line is equal to zero) to any date on the chart for which there is data history. If left blank, the date will default to the earliest available date for the two data histories.
The advantage of Relative Strength over Price Ratio is that the line does not reset every time you vary the chart time period. This is important if you are going to draw trendlines or captions.
Relative Strength Trading Signals
The Relative Strength indicator is not identical to the Relative Strength on Mansfield Charts — popularized by Stan Weinstein in his book Secrets For Profiting In Bull And Bear Markets. It is, however, very similar and can be used with Weinstein's long-term breakout system.
EXAMPLE
Apple is compared to the NASDAQ 100 index using Relative Strength and Price Ratio indicators.
The two lines are the same, except that Price Ratio is zero at the start of the chart, while Relative Strength is zero at the intercept date (2-Jan-2009). The difference is that you can plot trendlines on the Relative Strength indicator.
Formula
The Price Ratio is calculated using the ratio of closing price to that of another security, on the first day of the chart. This means that the starting point of the Price Ratio will vary according to the Time Period selected. The line may appear to move if you change time periods, but the slope remains the same.
Tip
Settle on one or two standard time periods to be used when viewing Price Ratios (eg. 3 Years - Weekly; 6 Months - Daily).
The steps required to calculate the Price Ratio are best illustrated by an example: Calculate the Price Ratio of IBM to the Dow Jones Industrial Average (DJI)-
1. Calculate the Inverse Ratio on Day 1: DJI divided by IBM.
2. Divide IBM by DJI each day
3. Then multiply step 2 by the Inverse Ratio in step 1
4. The Price Ratio then reduces the start to zero by subtracting 1 (from step 3).
Note: Metastock ® use a different formula to normalize to zero. They calculate the ratio in step 2 and then subtract the ratio on day 1 from each subsequent day. The results are similar.
Relative Strength Formula
Relative Strength is calculated as follows:
• Determine the Intercept Ratio — the ratio between the closing price of the two data sets on the specified intercept date.
• Determine the closing price ratio on the current date (stock 1/stock 2).
• Multiply the result by the Intercept Ratio and subtract 1.
Relative Strength is plotted using the ratio of closing price to that of another stock or index, on the date specified or the default date, whichever is the later. The default date is taken as the earliest possible date (i.e. the commencement date of the shorter of the two data histories). For example, if we plot the price ratio of Microsoft against the S&P 500 the default date will be 01-Jun-1993, the start of the Microsoft data history, which is later than the 02-Jan-1980 start of the S&P 500 data series.
本文翻譯由兄弟財經提供
文章來源：http://www.incrediblecharts.com/indicators/price_ratio.php