Why does the "quality/new goods bias" arise if we calculate the inflation rate based on a fixed basket of goods?

The inflation rate is the percentage increase in the average price level of goods and services over a specific period of time, typically measured on a year-over-year basis. A common method for calculating the inflation rate is using a fixed basket of goods, which represents the typical items that households purchase. The fixed basket of goods is used as a reference for the cost of living and to calculate the Consumer Price Index (CPI).

The quality/new goods bias is a distortion in the measurement of inflation due to changes in the quality of goods and the introduction of new goods in the market. This bias arises because the fixed basket of goods does not automatically account for the improvements in the quality of goods or the addition of new goods that may be replacing older, less efficient products.

When measuring inflation using a fixed basket of goods, the price changes are tracked for each item in the basket. However, over time, the quality of the items in the basket may improve, leading to higher prices for the improved products. If the price increase is due to an improvement in quality, it doesn't necessarily represent a true increase in the cost of living. Conversely, if the quality of a product declines but the price remains the same, this could actually represent an increase in inflation, as consumers receive less value for the same price. Similarly, as new goods are introduced into the market, they may replace older or less efficient products. These new goods could offer a better value for consumers, but because they are not included in the fixed basket of goods, the CPI and the inflation rate calculated based on this basket will not accurately reflect the change in the costs of these new goods.

In conclusion, the "quality/new goods bias" arises when calculating the inflation rate based on a fixed basket of goods because the basket may not fully account for improvements in the quality of goods or the introduction of new goods into the market. This can lead to a distortion in the measurement of inflation, as the changes in the cost of living are not accurately reflected. As a result, alternative methods of measuring inflation, such as using chained price indexes or hedonic pricing models, may help to better account for these biases.