Measuring economic developments is often a laborious business. Consider, for example, the Consumer Price Index (CPI). One first has to define the so called consumption basket that contains the goods and services whose prices you want to track. These goods and services have to be represented in the basket in the right proportions, reflecting the consumption patterns of an average consumer. Unfortunately, consumption habits change over time, and product characteristics change even more. A personal computer 10 years ago is obviously a very different object ...