中文段落：

价格指数，又称物价指数，是用来衡量一篮子商品和服务价格水平随时间变化的统计指标。它反映了市场上商品和服务的总体价格变动情况，常被用作衡量通货膨胀或通货紧缩的重要指标。价格指数的编制通常基于一定的商品和服务篮子，这些商品和服务的选取需要具有代表性和广泛性，能够反映整体经济活动的价格变动。

价格指数的计算方法有多种，常见的有简单平均法、加权平均法以及几何平均法等。在计算时，首先需要确定基期，即价格基准点，然后将各期价格与基期价格进行比较，得出各期价格指数。价格指数的变化可以显示出经济活动的活跃程度、货币政策的效果以及市场供需关系的变化。

通过价格指数，人们可以更加直观地了解经济运行情况，为政策制定和投资决策提供参考。例如，在通货膨胀期间，价格指数上升，表明货币购买力下降，这时政策制定者可能会调整货币政策，控制通货膨胀。对于投资者而言，价格指数的变动也会影响其投资决策，例如，在物价上涨较快的情况下，投资者可能会更倾向于投资实物资产以保值增值。

英文段落：

The price index, also known as the consumer price index (CPI), is a statistical measure that tracks changes in the price level of a basket of goods and services over time. It reflects the overall price movement of goods and services in the market and is often used as a key indicator to measure inflation or deflation. The compilation of the price index is typically based on a representative and diverse basket of goods and services that can reflect the price changes in the overall economic activity.

There are several methods for calculating the price index, including the simple average method, weighted average method, and geometric average method. When calculating the price index, a base period, or a price benchmark, is first determined. Then, the prices in each period are compared to the prices in the base period to derive the price index for each period. Changes in the price index can indicate the level of economic activity, the effectiveness of monetary policy, and changes in market supply and demand relationships.

Through the price index, people can gain a more intuitive understanding of economic conditions, providing reference for policy making and investment decisions. For example, during inflation, when the price index rises, indicating a decrease in the purchasing power of money, policymakers may adjust monetary policy to control inflation. For investors, changes in the price index can also affect their investment decisions. For instance, in a situation of rapid price increases, investors may be more inclined to invest in physical assets to preserve and increase their value.