United States - CPI: Urban Consumer - Butter and margarine

The U.S. Bureau of Labor Statistics (BLS) reports monthly consumer price indices (CPI) for the United States. CPI measures the change in prices paid by consumers for goods and services. Figures are reported using various bases, both seasonally adjusted (SA) and not seasonally adjusted (NSA).

• Classification: Specific to this dataset
• Measurements:
  • Fixed-base index relative to 36-month interval 1982 to 1984 (Index 1982-84=100)
  • (Index Nov1982=100)
  • (Index Dec1982=100)
  • (Index Dec1983=100)
  • (Index Dec1984=100)
  • (Index Dec1986=100)
  • (Index Dec1990=100)
  • (Index Dec1997=100)
  • (Index Dec2009=100)
  • (Index Dec2017=100)
  • Contribution to growth (%)
• Adjustments:
  • Seasonally adjusted (SA)
  • Not seasonally adjusted (SA)
• Native frequency: Monthly
• Start date: As early as 1913m1
• Geo coverage:
  • Country
  • Census regions and divisions (13x C^^^)
  • Select MSAs (23x IUSA_M^^^)
  • BLS city size classes (CTY_^, CTY_^^, C^^^_^)
• All concept-geo pairs exist: No

The BLS reports CPI for two different population groups:

1. Urban consumers (CPI-U): all residents of the urban or metropolitan areas which include professionals, self-employed, the poor, the unemployed, retirees, and urban wage earners and clerical worker. This group represents approximately 94% of the total U.S. population. Those not included in this group are those living in rural nonmetroplitan areas, farming families, Armed Forces and those in institutions (prisons and mental hospitals).
2. Urban Wage Earners and Clerical Workers (CPI-W): all households that meet the following requirements: more than one half of the household's income comes from clerical or wage occupations AND at least one of the household's earners have been employed for at least 37 weeks during the previous 12 months. This group represents approximately 28% of the total U.S. population and is a subset of urban consumers.

Data is collected each month in 75 urban areas in the United States. There are about 5,000 housing units and 22,000 retail establishments sampled. Taxes associated with the purchase of goods or services are included in the price and index. Data is typically collected by personal visits or phone calls by BLS representatives.

The index is calculated by aggregation and using weights for each items in a specific location. The weights represent their importance in the spending for each population group. Localized data is then combined to calulcate a U.S. city average. 

Area indexes do not measure differences in the level of prices among cities; they only measure the average change in prices for each area since the base period.

The indexes have a base of 1982-84=100, unless otherwise noted. This means that the average of the monthly index values is 100 over the 36 months in 1982 through 1984.  An index represents the relative change over time since a base period. For example, an index of 120 denotes an increase of 20%, and 75 is a decrease of 25%.

There are various base periods in this data set depending on the type of expenditure and geographical area. The base periods are: Oct1967, Jan1978, Feb1978, Apr1978, Nov1977, Dec1977, 1982-84, Nov1982, Dec1982, Dec1983, Nov1984, Dec1986, Dec1988, Nov1996, Dec1996, Nov1997, Dec1997, Dec2005, Dec2007, Dec2009, and Dec2017.

Geographic coverage is all four census regions, all nine census divisions, 23 MSAs per Census 2010 delineations, and 10 class-sizes (population groups by area).

Seasonally adjusted (SA) data are computed using seasonal factors derived by the X-13ARIMA-SEATS seasonal adjustment method. Factors are updated each February, and are used used to revise the previous five years of SA series.

Frequency

• Prices of fuels are obtained each month in all 75 areas. 
• Commodity and services prices are reported each month for the three largest CBSA mertro geographic areas (Chicago-Naperville-Elgin, IL-IN-WI, New York-Newark-Jersey City, NY-NJ-PA, and Los Angeles-Long Beach-Anaheim, CA).
• National, Regional, and Divisional level data is updated monthly.
• All other CBSA metros are reported bimonthly (varies even/odd month for each geo). See Table 2: https://www.bls.gov/cpi/additional-resources/geographic-revision-2018.htm

Geographies

Moody's Analytics supplements

As of January 2022, we compute two special metrics related to the COVID-19 pandemic. viz., the contributions to CPI-U growth of two groups of items: those that are constrained by supply chains, and those associated with pandemic reopening.

As of June 2022, we calculate the contribution to CPI-U growth for 30 major expenditure items.

Yes, when expenditure weights are updated.

Yes, when seasonal factors are updated. This is performed prior to the release of January data, and applies to the prior five years. The source writes:

The Consumer Price Index (CPI) produces both unadjusted and seasonally adjusted data. Seasonally adjusted data are computed using seasonal factors derived by the X-13ARIMA-SEATS Seasonal Adjustment Method. These factors are updated with the release of January data in February and reflect price movements from the previous calendar year. The new factors are used to revise the previous 5 years of seasonally adjusted data; older seasonally adjusted indexes are considered to be final.

Topline year over year calculations are reported in the BLS press releases as non-seasonally adjusted (XCPIU.IUSA). There may be slight differences between Y/Y figures for SA and NSA series. Because the seasonal factors differ each year, the ratio of index numbers used to compute the change are not necessarily exactly comparable.

Further reading

At the source:

• BLS FAQs
• Seasonal Adjustment
• BLS Methodology
• Geographies
• Handbook of Methods
• Item definitions