价格比率或相对强度指标与价格对比的目的相同——它比较了一只股票相对于另外一只股票（或指数）的表现。一些交易者将价格比率指标作为寻找突出表现股票的一种常用的工具。
价格比率的计算方法是：第一只股票的收盘价 / 第二只股票的收盘价。
与价格对比不同的是，价格比率是呈现在一个单独的指标窗口。有以下三种可以选择：
1. 调整后的价格比率：指标线总是从图表的左侧零处开始。
2. 价格比率（未调整）：简单的表现出两只股票收盘价之间的原始关系。
3. 相对强度与价格比率类似，不同的是，你可以截取任一时间段的价格走势（该段走势在相对强度窗口从零处开始显示）。如果不指定周期的话，价格比率会默认为比较两只股票所有的价格走势。
相对强度指标与价格比率相比的优势在于，你不必在每次改变图表周期之后重新设置。如果你打算绘制出趋势线或者添加备注，这一点很重要。
相对强度的交易信号
温斯坦的《称傲牛熊市的秘密》一书中，曼斯菲尔德图表关于相对强度指标与相对强度的描述并不完全一致。它们十分的相似，并且都可以与温斯坦的长期突破交易系统结合使用。
示例
利用相对强度以及价格比率指标对比苹果公司股票与纳斯达克100指数。
下面的两条直线走势是一致的：，价格比率是从零处开始，而相对强度指标的零点则是从所选起点处开始，2009年1月2日处为零。不同之处在于，你可以在相对强度指标上画出趋势线。
价格比率的计算公式
价格比率是通过一个股票的收盘价比率比上另一只股票的收盘价比率得出，从图表的第一天开始。意思是，所选的时间周期不同，价格比率的起始点会相应变化，如果你变换时间周期，价格比率曲线似乎是在移动，但是形态会保持一致。
建议
浏览价格比率的时候，设置一个或两个时间周期作为参照标准（比如，3年-周；6个月-日）。
计算价格比率的方法可以按照下面计算IBM与DJI（道琼斯工业指数）的价格比率的步骤。
1. 计算出第一日价格比率的反比： DJI / IBM.
2. 每日都计算出IBM / DJI 的值。
3. 第一步的值*第二步的值。
4. 第三步的值减去1，即可使价格比率起始点位于零点。
示例
注意：另外一种使起点为零的方法是计算出第二步的比值，接下来每一日的比值都减去第一步的值。这种方法的结果类似于上面例子。
价格相对强度的计算公式
1、 确定所截取数据的价格比率：所截取周期内两只股票的收盘价比值。
2、 确认当前两只股票的收盘价比值（股票1的收盘价/股票2的收盘价）。
3、 步骤1乘以步骤2，再减去1
相对强度指标是在所截取时间段内或默认时间内，利用一只股票的收盘价比率与另一只股票或指数的收盘价比率计算而来。默认的时间段是两只股票上市以来的所有价格走势数据。比如，如果我们对比微软公司与标普500指数的价格相对强度，那么微软公司的起始时间是1993年6月1日，早于标普500指数的起始时间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.
本文翻译由兄弟财经提供
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