The index is a ratio that compares the total purchase cost of a specified bundle of current-period commodities (commodities valued at current prices) with the value of those same commodities at base-period prices; this ratio is multiplied by 100. The Paasche price index tends to understate price increases, since it already reflects some of the changes in consumption patterns that occur when consumers respond to price increases—i.e., increased consumption of goods will indicate reduced relative prices.