The CPI-W is the basis for any Social Security COLA. Some people do not believe it is a fair reflection of the cost of living. Others have commented that it does not include food and other key items in the mix.
Here is an explanation from the Bureau of Labor Statistics.
What goods and services does the CPI cover?
The CPI represents all goods and services purchased for consumption by the reference population (U or W) BLS has classified all expenditure items into more than 200 categories, arranged into eight major groups.
Major groups and examples of categories in each are as follows:
FOOD AND BEVERAGES (breakfast cereal, milk, coffee, chicken, wine, full service meals, snacks)
HOUSING (rent of primary residence, owners’ equivalent rent, fuel oil, bedroom furniture)
APPAREL (men’s shirts and sweaters, women’s dresses, jewelry)
TRANSPORTATION (new vehicles, airline fares, gasoline, motor vehicle insurance)
MEDICAL CARE (prescription drugs and medical supplies, physicians’ services, eyeglasses and eye care, hospital services)
RECREATION (televisions, toys, pets and pet products, sports equipment, admissions);
EDUCATION AND COMMUNICATION (college tuition, postage, telephone services, computer software and accessories);
OTHER GOODS AND SERVICES (tobacco and smoking products, haircuts and other personal services, funeral expenses).
Also included within these major groups are various government-charged user fees, such as water and sewerage charges, auto registration fees, and vehicle tolls. In addition, the CPI includes taxes (such as sales and excise taxes) that are directly associated with the prices of specific goods and services. However, the CPI excludes taxes (such as income and Social Security taxes) not directly associated with the purchase of consumer goods and services.
The CPI does not include investment items, such as stocks, bonds, real estate, and life insurance. (These items relate to savings and not to day-to-day consumption expenses.)