Consumer Price Index Summary

Transmission of material in this release is embargoed until                                        
8:30 a.m. (ET) Thursday, October 10, 2024      USDL-24-2101
	
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CONSUMER PRICE INDEX - SEPTEMBER 2024

The Consumer Price Index for All Urban Consumers (CPI-U) increased 0.2 percent on a seasonally adjusted
basis, the same increase as in August and July, the U.S. Bureau of Labor Statistics reported today. Over
the last 12 months, the all items index increased 2.4 percent before seasonal adjustment.

The index for shelter rose 0.2 percent in September, and the index for food increased 0.4 percent. Together,
these two indexes contributed over 75 percent of the monthly all items increase. The food at home index
increased 0.4 percent in September and the food away from home index rose 0.3 percent over the month. The
energy index fell 1.9 percent over the month, after declining 0.8 percent the preceding month.

The index for all items less food and energy rose 0.3 percent in September, as it did the preceding month.
Indexes which increased in September include shelter, motor vehicle insurance, medical care, apparel, and
airline fares. The indexes for recreation and communication were among those that decreased over the month.

The all items index rose 2.4 percent for the 12 months ending September, the smallest 12-month increase
since February 2021. The all items less food and energy index rose 3.3 percent over the last 12 months.
The energy index decreased 6.8 percent for the 12 months ending September. The food index increased 2.3
percent over the last year. 

Food

The food index increased 0.4 percent in September, after rising 0.1 percent in August. The index for food
at home also rose 0.4 percent in September. Five of the six major grocery store food group indexes increased
over the month. The index for meats, poultry, fish, and eggs rose 0.8 percent in September as the index
for eggs increased 8.4 percent. The fruits and vegetables index increased 0.9 percent over the month,
following a 0.2-percent decline in August. The index for other food at home rose 0.2 percent in September
and the index for cereals and bakery products increased 0.3 percent. The dairy and related products index
increased 0.1 percent over the month, while the nonalcoholic beverages index was unchanged in September.

The food away from home index rose 0.3 percent in September, as it did in August. The index for full service
meals rose 0.4 percent and the index for limited service meals increased 0.2 percent over the month.

The index for food at home rose 1.3 percent over the last 12 months. The meats, poultry, fish, and eggs
index rose 3.9 percent over the last 12 months and the nonalcoholic beverages index increased 1.3 percent.
Over the same period, the index for fruits and vegetables rose 0.7 percent and the index for other food at
home increased 0.4 percent. The dairy and related products index increased 0.5 percent in September, and
the cereals and bakery products index increased 0.1 percent over the year.

The food away from home index rose 3.9 percent over the last year. The index for limited service meals
increased 4.1 percent over the last 12 months and the index for full service meals rose 3.9 percent over
the same period. 

Energy

The energy index fell 1.9 percent in September, after declining 0.8 percent in August. The gasoline index
decreased 4.1 percent over the month. (Before seasonal adjustment, gasoline prices decreased 5.1 percent
in September.) The electricity index increased 0.7 percent over the month, as did the natural gas index.

The energy index decreased 6.8 percent over the past 12 months. The gasoline index fell 15.3 percent over
this 12-month span, and the fuel oil index fell 22.4 percent over that period. In contrast, the index for
electricity increased 3.7 percent over the last 12 months, and the index for natural gas rose 2.0 percent. 

All items less food and energy

The index for all items less food and energy rose 0.3 percent in September, as it did in August. The shelter
index increased 0.2 percent in September. The index for owners' equivalent rent and the index for rent
both rose 0.3 percent over the month. The lodging away from home index fell 1.9 percent in September,
after rising 1.8 percent in August. 

The medical care index increased 0.4 percent over the month after declining in each of the previous 2 months.
The index for physicians' services increased 0.9 percent in September. In contrast, the prescription drugs
index declined 0.5 percent over the month.

The motor vehicle insurance index rose 1.2 percent in September, following a 0.6-percent increase the
previous month. The index for apparel increased 1.1 percent over the month and the index for airline fares
rose 3.2 percent in September. The indexes for education, household furnishings and operations, personal
care, used cars and trucks, and new vehicles also increased in September.

The index for recreation fell 0.4 percent in September, following a 0.1-percent decrease the preceding month.
The communication index decreased 0.6 percent over the month, also following a 0.1-percent decline in August. 

The index for all items less food and energy rose 3.3 percent over the past 12 months. The shelter index
increased 4.9 percent over the last year, accounting for over 65 percent of the total 12-month increase
in the all items less food and energy index. Other indexes with notable increases over the last year
include motor vehicle insurance (+16.3 percent), medical care (+3.3 percent), personal care (+2.5 percent),
and apparel (+1.8 percent).

Not seasonally adjusted CPI measures

The Consumer Price Index for All Urban Consumers (CPI-U) increased 2.4 percent over the last 12 months to
an index level of 315.301 (1982-84=100). For the month, the index increased 0.2 percent prior to seasonal
adjustment.  

The Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W) increased 2.2 percent over
the last 12 months to an index level of 309.046 (1982-84=100). For the month, the index increased 0.1
percent prior to seasonal adjustment.  

The Chained Consumer Price Index for All Urban Consumers (C-CPI-U) increased 2.3 percent over the last 12
months. For the month, the index increased 0.1 percent on a not seasonally adjusted basis. Please note that
the indexes for the past 10 to 12 months are subject to revision. 
_______________
The Consumer Price Index for October 2024 is scheduled to be released on Wednesday, November 13, 2024,
at 8:30 a.m. (ET).




Technical Note

Brief Explanation of the CPI
The Consumer Price Index (CPI) measures the change in prices paid by consumers for goods and services.
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 over 90 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, farming 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). 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 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 approximately 30
percent of the total U.S. population and is a subset of the CPI-U population.

The CPIs are based on prices of food, clothing, shelter, fuels, transportation, doctors' and dentists'
services, drugs, and other goods and services that people buy for day-to-day living. Prices are
collected each month in 75 urban areas across the country from about 6,000 housing units and
approximately 22,000 retail establishments (department stores, supermarkets, hospitals, filling
stations, and other types of stores and service establishments). All taxes directly associated with the
purchase and use of items are included in the index. Prices of fuels and a few other items are obtained
every month in all 75 locations. Prices of most other commodities and services are collected every
month in the three largest geographic areas and every other month in other areas. Prices of most goods
and services are obtained by personal visit, telephone call, web, or app collection by the Bureau's
trained representatives.

In calculating the index, price changes for the various items in each location are aggregated using
weights, which represent their importance in the spending of the appropriate population group. Local
data are then combined to obtain a U.S. city average. For the CPI-U and CPI-W, separate indexes are
also published by size of city, by region of the country, for cross-classifications of regions and
population-size classes, and for 23 selected local areas. 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. For the C-CPI-U, data are issued only at the national level. The CPI-U and CPI-W are
considered final when released, but the C-CPI-U is issued in preliminary form and subject to three
subsequent quarterly revisions.

The index measures price change from a designed reference date. For most of the CPI-U and the CPI-W,
the reference base is 1982-84 equals 100. The reference base for the C-CPI-U is December 1999 equals
100.  An increase of 7 percent from the reference base, for example, is shown as 107.000. Alternatively,
that relationship can also be expressed as the price of a base period market basket of goods and
services rising from $100 to $107. 

Sampling Error in the CPI

The CPI is a statistical estimate that is subject to sampling error because it is based upon a sample
of retail prices and not the complete universe of all prices. BLS calculates and publishes estimates
of the 1-month, 2-month, 6-month, and 12-month percent change standard errors annually for the CPI-U.
These standard error estimates can be used to construct confidence intervals for hypothesis testing.
For example, the estimated standard error of the 1-month percent change is 0.03 percent for the U.S.
all items CPI. This means that if we repeatedly sample from the universe of all retail prices using
the same methodology, and estimate a percentage change for each sample, then 95 percent of these
estimates will be within 0.06 percent of the 1-month percentage change based on all retail prices. For
example, for a 1-month change of 0.2 percent in the all items CPI-U, we are 95 percent confident that
the actual percent change based on all retail prices would fall between 0.14 and 0.26 percent. For the
latest data, including information on how to use the estimates of standard error, 
see www.bls.gov/cpi/tables/variance-estimates/home.htm. 

Calculating Index Changes

Movements of the indexes from 1 month to another are usually expressed as percent changes rather than
changes in index points, because index point changes are affected by the level of the index in relation
to its base period, while percent changes are not. The following table shows an example of using index
values to calculate percent changes:

                            Item A                  Item B                      Item C
Year I                      112.500                 225.000                     110.000
Year II                     121.500                 243.000                     128.000
Change in index points      9.000                   18.000                      18.000
Percent change              9.0/112.500 x 100 = 8.0  18.0/225.000 x 100 = 8.0   18.0/110.000 x 100 = 16.4

Use of Seasonally Adjusted and Unadjusted Data

The Consumer Price Index (CPI) program 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 each February, and the new factors are used to revise the
previous 5 years of seasonally adjusted data. The factors are available at 
www.bls.gov/cpi/tables/seasonal-adjustment/seasonal-factors-2024.xlsx. For more information on data
revision scheduling, please see the Factsheet on Seasonal Adjustment at 
www.bls.gov/cpi/seasonal-adjustment/questions-and-answers.htm and the Timeline of Seasonal Adjustment
Methodological Changes at www.bls.gov/cpi/seasonal-adjustment/timeline-seasonal-adjustment-methodology-changes.htm. 

How to Use Seasonally Adjusted and Unadjusted Data

For analyzing short-term price trends in the economy, seasonally adjusted changes are usually preferred
since they eliminate the effect of changes that normally occur at the same time and in about the same
magnitude every year-such as price movements resulting from weather events, production cycles, model
changeovers, holidays, and sales. This allows data users to focus on changes that are not typical for
the time of year. 

The unadjusted data are of primary interest to consumers concerned about the prices they actually pay.
Unadjusted data are also used extensively for escalation purposes. Many collective bargaining contract
agreements and pension plans, for example, tie compensation changes to the Consumer Price Index before
adjustment for seasonal variation. BLS advises against the use of seasonally adjusted data in
escalation agreements because seasonally adjusted series are revised annually for five years.

Intervention Analysis

The Bureau of Labor Statistics uses intervention analysis seasonal adjustment (IASA) for some CPI
series. Sometimes extreme values or sharp movements can distort the underlying seasonal pattern of
price change. Intervention analysis seasonal adjustment is a process by which the distortions caused by
such unusual events are estimated and removed from the data prior to calculation of seasonal factors.
The resulting seasonal factors, which more accurately represent the seasonal pattern, are then applied
to the unadjusted data.

For example, this procedure was used for the motor fuel series to offset the effects of the 2009 return
to normal pricing after the worldwide economic downturn in 2008. Retaining this outlier data during 
seasonal factor calculation would distort the computation of the seasonal portion of the time series
data for motor fuel, so it was estimated and removed from the data prior to seasonal adjustment.
Following that, seasonal factors were calculated based on this "prior adjusted" data. These seasonal
factors represent a clearer picture of the seasonal pattern in the data. The last step is for motor
fuel seasonal factors to be applied to the unadjusted data.

For the seasonal factors introduced for January 2024, BLS adjusted 46 series using intervention
analysis seasonal adjustment, including selected food and beverage items, motor fuels and vehicles.

Revision of Seasonally Adjusted Indexes

Seasonally adjusted data, including the U.S. city average all items index levels, are subject to
revision for up to 5 years after their original release. Every year, economists in the CPI calculate
new seasonal factors for seasonally adjusted series and apply them to the last 5 years of data.
Seasonally adjusted indexes beyond the last 5 years of data are considered to be final and not subject
to revision. For January 2024, revised seasonal factors and seasonally adjusted indexes for 2019 to
2023 were calculated and published. For series which are directly adjusted using the Census
X-13ARIMA-SEATS seasonal adjustment software, the seasonal factors for 2023 will be applied to data for
2024 to produce the seasonally adjusted 2024 indexes. Series which are indirectly seasonally adjusted
by summing seasonally adjusted component series have seasonal factors which are derived and are
therefore not available in advance.

Determining Seasonal Status

Each year the seasonal status of every series is reevaluated based upon certain statistical criteria.
Using these criteria, BLS economists determine whether a series should change its status from "not
seasonally adjusted" to "seasonally adjusted", or vice versa. If any of the 81 components of the U.S.
city average all items index change their seasonal adjustment status from seasonally adjusted to not
seasonally adjusted, not seasonally adjusted data will be used in the aggregation of the dependent
series for the last 5 years, but the seasonally adjusted indexes before that period will not be changed.
For 2024, 36 of the 81 components of the U.S. city average all items index are not seasonally adjusted.

Contact Information

For additional information about the CPI visit www.bls.gov/cpi or contact the CPI Information and
Analysis Section at 202-691-7000 or cpi_info@bls.gov. 

For additional information on seasonal adjustment in the CPI visit www.bls.gov/cpi/seasonal-adjustment/home.htm

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