什麼是物價指數

一組價格的變化量數，包含一系列數字，目的是要對兩個時間或地點之物價進行比較，以顯示兩個時間的物價變化、或兩個地點的物價差異。物價指數是最早發展出來的生活支出變化量數，爲的是要決定如何調整可維持基本生活水準（standard of living）的工資。物價指數主要有兩類，第一類是拉斯皮爾制定的拉氏指數（Laspeyres-type indexes），先選定某一基期內的財貨市場組合，再利用其物價來檢定該財貨在不同時空的物價變化，計算出該財貨今日價格和基期價格的比例。拉氏法有兩種最常用的指數，分別是消費者物價指數（consumer price index,CPI）和生產物價指數（producer price index, PPI），其中生產物價指數舊稱躉售物價指數（wholesale price index）。CPI測量基本財貨（如食、衣、住）零售物價的變化，PPI則測量製造廠和躉售商出貨價格的變化。第二種是裴奇所制定的裴氏指數（Paasche-type indexes），先選定當前的財貨市場組合，再利其物價來檢定過去時間同樣財貨的物價變化；裴氏法最常用的指數是國內生產毛額平減指數（GDP deflator），在美國用於國民收入會計，以計算經常貨幣總額與當前貨幣總額的差異。

price index

Measure of change in a set of prices, consisting of a series of numbers arranged so that a comparison of the values for any two periods or places will show the change in prices between periods or the difference in prices between places. Price indexes were first developed to measure changes in the cost of living in order to determine the wage increases necessary to maintain a constant standard of living. There are two basic types. Laspeyres-type indexes define a market basket of goods in a base period, then use the prices for those goods to examine change over space and time. In its simplest form, this is simply the ratio of what those goods cost today to what they cost in the base period. The two most familiar indexes of this type are the consumer price index (CPI) and the producer price index (PPI). The CPI measures changes in retail prices in such component parts as food, clothing, and shelter. The PPI (formerly called the wholesale price index) measures changes in the prices charged by manufacturers and wholesalers. Paasche-type indexes define a market basket of goods in the current period, then use the prices of those goods from past periods. The most familiar index of this type is the GDP deflator, used in the U.S. in the national income accounting to differentiate amounts in constant dollars from those in current dollars.