BLS has for some time used a cost-of-living framework in making practical decisions about questions that arise in constructing the CPI.
A cost-of-living index would measure changes over time in the amount that consumers need to spend to reach a certain utility level or standard of living.
Both the CPI and a cost-of-living index would reflect changes in the prices of goods and services, such as food and clothing that are directly purchased in the marketplace; but a complete cost-of-living index would go beyond this to also take into account changes in other governmental or environmental factors that affect consumers' well-being.
It is very difficult to determine the proper treatment of public goods, such as safety and education, and other broad concerns, such as health, water quality, and crime that would constitute a complete cost-of-living framework.
However, more practical formulas can be evaluated based on their relationship to the true cost of living index.