Data available
·         Price indexes are available for the U.S., the four Census regions, size of city, cross-classifications of regions and size-classes, and for 26 local areas. Indexes are available for major groups of consumer expenditures (food and beverages, housing, apparel, transportation, medical care, recreation, education and communications, and other goods and services), for items within each group, and for special categories, such as services.
·         Monthly indexes are available for the U.S., the four Census regions, and some local areas. More detailed item indexes are available for the U.S. than for regions and local areas.
·         Indexes are available for two population groups: a CPI for All Urban Consumers (CPI-U) which covers approximately 87 percent of the total population and a CPI for Urban Wage Earners and Clerical Workers (CPI-W) which covers 32 percent of the population.
·         Some series, such as the U.S. City Average All items index, begin as early as 1913.

What is the CPI?

The Consumer Price Index (CPI) is a measure of the average change over time in the prices paid by urban consumers for a market basket of consumer goods and services.
Whose buying habits does the CPI reflect?
The CPI reflects spending patterns for each of two population groups: all urban consumers and urban wage earners and clerical workers. The all urban consumer group represents about 87 percent of the total U.S. population. It is based on the expenditures of almost all residents of urban or metropolitan areas, including professionals, the self-employed, the poor, the unemployed, and retired people, as well as urban wage earners and clerical workers. Not included in the CPI are the spending patterns of people living in rural nonmetropolitan areas, farm families, people in the Armed Forces, and those in institutions, such as prisons and mental hospitals. Consumer inflation for all urban consumers is measured by two indexes, namely, the Consumer Price Index for All Urban Consumers (CPI-U) and the Chained Consumer Price Index for All Urban Consumers (C-CPI-U). ( See the answer to Question 4 for an explanation of the differences between the CPI-U and C-CPI-U.)
The Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W) is based on the expenditures of households included in the CPI-U definition that also meet two requirements: more than one-half of the household's income must come from clerical or wage occupations, and at least one of the household's earners must have been employed for at least 37 weeks during the previous 12 months. The CPI-W population represents about 32 percent of the total U.S. population and is a subset, or part, of the CPI-U population.
Is the CPI a cost-of-living index?
The CPI frequently is called a cost-of-living index, but it differs in important ways from a complete cost-of-living measure. 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 is a conceptual measurement goal, however, and not a straightforward alternative to 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 role 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. More.
Does the CPI measure my experience with price change?
Not necessarily. It is important to understand that BLS bases the market baskets and pricing procedures for the CPI-U and CPI-W populations on the experience of the relevant average household, not of any specific family or individual. It is unlikely that your experience will correspond precisely with either the national indexes or the indexes for specific cities or regions. More.
How is the CPI market basket determined?
The CPI market basket is developed from detailed expenditure information provided by families and individuals on what they actually bought.  For the current CPI, this information was collected from the Consumer Expenditure Surveys for 2007 and 2008. In each of those years, about 7,000 families from around the country provided information each quarter on their spending habits in the interview survey.  To collect information on frequently purchased items, such as food and personal care products, another 7,000 families in each of these years kept diaries listing everything they bought during a 2-week period.
Over the 2 year period, then, expenditure information came from approximately 28,000 weekly diaries and 60,000 quarterly interviews used to determine the importance, or weight, of the more than 200 item categories in the CPI index structure.
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.)
How are CPI prices collected and reviewed?
Each month, BLS data collectors called economic assistants visit or call thousands of retail stores, service establishments, rental units, and doctors' offices, all over the United States, to obtain information on the prices of the thousands of items used to track and measure price changes in the CPI. These economic assistants record the prices of about 80,000 items each month, representing a scientifically selected sample of the prices paid by consumers for goods and services purchased.
During each call or visit, the economic assistant collects price data on a specific good or service that was precisely defined during an earlier visit. If the selected item is available, the economic assistant records its price. If the selected item is no longer available, or if there have been changes in the quality or quantity (for example, eggs sold in packages of ten when they previously were sold by the dozen) of the good or service since the last time prices were collected, the economic assistant selects a new item or records the quality change in the current item.
The recorded information is sent to the national office of BLS, where commodity specialists who have detailed knowledge about the particular goods or services priced review the data. These specialists check the data for accuracy and consistency and make any necessary corrections or adjustments, which can range from an adjustment for a change in the size or quantity of a packaged item to more complex adjustments based upon statistical analysis of the value of an item's features or quality. Thus, commodity specialists strive to prevent changes in the quality of items from affecting the CPI's measurement of price change.
How is the CPI calculated?
The CPI is a product of a series of interrelated samples. First, using data from the 1990 Census of Population, BLS selected the urban areas from which data on prices were collected and chose the housing units within each area that were eligible for use in the shelter component of the CPI. The Census of Population also provided data on the number of consumers represented by each area selected as a CPI price collection area. Next, another sample (of about 14,500 families each year) served as the basis for a Point-of-Purchase Survey that identified the places where households purchased various types of goods and services. More.
How are taxes treated in the CPI?
Certain taxes are included in the CPI, namely, taxes that are directly associated with the purchase of specific goods and services (such as sales and excise taxes). Government user fees are also included in the CPI. For example, toll charges and parking fees are included in the transportation category, and an entry fee to a national park would be included as part of the admissions index. In addition, property taxes should be reflected indirectly in the BLS method of measuring the cost of the flow of services provided by shelter, which we called owners' equivalent rent, to the extent that these taxes influence rental values. Taxes not directly associated with specific purchases, such as income and Social Security taxes, are excluded, as are the government services paid for through those taxes.
For certain purposes, one might want to define price indexes to include, rather than exclude, income taxes. Such indexes would provide an answer to a question different from the one to which the present CPI is relevant, and would be appropriate for different uses.
What are some limitations of the CPI?
The CPI is subject to both limitations in application and limitations in measurement.
Limitations of application
The CPI may not be applicable to all population groups.  For example, the CPI-U is designed to measure inflation for the U.S. urban population and thus may not accurately reflect the experience of people living in rural areas.  Also, the CPI does not produce official estimates for the rate of inflation experienced by subgroups of the population, such as the elderly or the poor. (BLS does produce and release an experimental index for the elderly population; however, because of the significant limitations of this experimental index, it should be interpreted with caution.)
As noted in the answer to question 19, the CPI cannot be used to measure differences in price levels or living costs between one place and another; it measures only time-to-time changes in each place. A higher index for one area does not necessarily mean that prices are higher there than in another area with a lower index. It merely means that prices have risen faster in the area with the higher index since the two areas' common reference period.
The CPI cannot be used as a measure of total change in living costs because changes in these costs are affected by (such as social and environmental changes and changes in income taxes) that are beyond the definitional scope of the index and so are excluded.
Limitations in measurement
Limitations in measurement can be grouped into two basic types, sampling errors and non-sampling errors.
Sampling errors. Because the CPI measures price changes based on a sample of items, the published indexes differ somewhat from what the results would be if actual records of all retail purchases by everyone in the index population could be used to compile the index. These estimating or sampling errors are limitations on the accuracy of the index, not mistakes in calculating the index. The CPI program has developed measurements of sampling error, which are updated and published annually on the CPI home page. The CPI sample design allocates the sample in a way that maximizes the accuracy of the index, given the funds available.
Non sampling errors. These errors occur from a variety of sources. Unlike sampling errors, they can cause persistent bias in measurements of the index. Nonsampling errors are caused by problems of price data collection, logistical lags in conducting surveys, difficulties in defining basic concepts and their operational implementation, and difficulties in handling the problems of quality change. Non-sampling errors can be far more hazardous to the accuracy of a price index than sampling errors. Hence, BLS expends much effort to minimize these errors. Highly trained personnel ensure the comparability of quality of items from period to period (see answer to question 8); collection procedures are extensively documented, and recurring audits are conducted. The CPI program has an ongoing research and evaluation program in order to identify and implement improvements in the index.
The CPI is the most widely used measure of inflation and is sometimes viewed as an indicator of the effectiveness of government economic policy. It provides information about price changes in the Nation's economy to government, business, labor, and private citizens and is used by them as a guide to making economic decisions. In addition, the President, Congress, and the Federal Reserve Board use trends in the CPI to aid in formulating fiscal and monetary policies.
The CPI and its components are used to adjust other economic series for price changes and to translate these series into inflation-free dollars. Examples of series adjusted by the CPI include retail sales, hourly and weekly earnings, and components of the National Income and Product Accounts.
An interesting example is the use of the CPI as a deflator of the value of the consumer's dollar to find its purchasing power. The purchasing power of the consumer's dollar measures the change in the value to the consumer of goods and services that a dollar will buy at different dates. In other words, as prices increase, the purchasing power of the consumer's dollar declines.
The CPI is often used to adjust consumers' income payments (for example, Social Security) to adjust income eligibility levels for government assistance and to automatically provide cost-of-living wage adjustments to millions of American workers. As a result of statutory action the CPI affects the income of millions of Americans. Over 50 million Social Security beneficiaries, and military and Federal Civil Service retirees, have cost-of-living adjustments tied to the CPI. In addition, eligibility criteria for millions of food stamp recipients, and children who eat lunch at school, are affected by changes in the CPI. Many collective bargaining agreements also tie wage increases to the CPI.
Another example of how dollar values may be adjusted is the use of the CPI to adjust the Federal income tax structure. These adjustments prevent inflation-induced increases in tax rates, an effect called bracket creep.
Traditionally, the CPI was considered an upper bound on a cost-of-living index in that the CPI did not reflect the changes in buying or consumption patterns that consumers would make to adjust to relative price changes. The ability to substitute means that the increase in the cost to consumers of maintaining their level of well-being tends to be somewhat less than the increase in the cost of the mix of goods and services they previously purchased.
Since January 1999, a geometric mean formula has been used to calculate most basic indexes within the CPI; in other words, the prices within most item categories (for example, apples) are averaged with the use of a geometric mean formula. This improvement moves the CPI closer to a cost-of-living measure, because the geometric mean formula allows for a modest amount of consumer substitution as relative prices within item categories change.
It is important to note that area CPIs cannot be used to compare levels of living costs or prices across areas. (See answer to Question 18: "Can the CPIs for individual areas be used to compare living costs among areas?")
For example, if you or your family spends a larger-than-average share of your budget on medical expenses, and medical care costs are increasing more rapidly than the cost of other items in the CPI market basket, your personal rate of inflation may exceed the increase in the CPI. Conversely, if you heat your home with solar energy, and fuel prices are rising more rapidly than other items, you may experience less inflation than the general population does. A national average reflects all the ups and downs of millions of individual price experiences. It seldom mirrors a particular consumer's experience.
This information enabled BLS to construct the CPI market basket of goods and services and to assign each item in the market basket a weight, or importance, based on total family expenditures. The final stage in the sampling process is the selection of the specific detailed item to be priced in each outlet. This is done in the field, using a method called disaggregation. For example, BLS economic assistants may be directed to price "fresh whole milk." Through the disaggregation process, the economic assistant selects the specific kind of fresh whole milk that will be priced in the outlet over time. By this process, each kind of whole milk is assigned a probability of selection, or weight, based on the amount the store sells. If, for example, Vitamin D homogenized milk in half-gallon containers makes up 70 percent of the sales of whole milk, and the same milk in quart containers accounts for 10 percent of all whole-milk sales, then the half-gallon container will be 7 times as likely to be chosen as the quart container. After probabilities are assigned, one type, brand, and container size of milk is chosen by an objective selection process based on the theory of random sampling. The particular kind of milk that is selected by disaggregation will continue to be priced each month in the same outlet.
In sum, price changes are weighted by the importance of the item in the spending patterns of the appropriate population group. The combination of all these factors gives a weighted measurement of price change for all items in all outlets, in all areas priced for the CPI.