Quality bias
Quality bias in price indices is a kind of mismeasurement if they do not incorporate data on the quality of goods from period to period, as well as their nominal price. Personal computers are a canonical case. Because of improvements in computer chips, greater and greater speeds and features have become available, without substantial increases in price. If only price information on personal computers were used, quality bias would cause growth in a consumer price index (CPI) to be overestimated, since an equivalent computer would actually be much cheaper in later periods. Determining quality Quality bias can work both ways. Faster computers with enhanced performance require greater memory and more expensive support software. Most personal computers were previously bundled with software, but now come only with a basic operating system and a requirement for the purchaser to purchase the bundled software after a "trial period", so the actual value per dollar is much lower. Obsolescence is built into most personal electronics, shortening their useful live, again lowering the actual value. All these issues make the quality bias tend to be negative rather than positive. As products and the manufacturing methodology advances, the cost of manufacture is expected to go down,