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CONSUMER PRICE INDEX – SEPTEMBER 2017
The Consumer Price Index for All Urban Consumers (CPI-U) rose 0.5 percent in
September on a seasonally adjusted basis, the U.S. Bureau of Labor Statistics
reported today. Over the last 12 months, the all items index rose 2.2 percent.
The gasoline index increased 13.1 percent in September and accounted for about
three-fourths of the seasonally adjusted all items increase. Other major
energy component indexes were mixed, and the food index rose slightly.
The index for all items less food and energy increased 0.1 percent in
September. The shelter index continued to increase, and the indexes for motor
vehicle insurance, recreation, education, and wireless telephone services also
rose. These increases more than offset declines in the indexes for new
vehicles, household furnishings and operations, medical care, and used cars
The all items index rose 2.2 percent for the 12 months ending September; the
12-month change has been accelerating since it was 1.6 percent in June. The
12-month change in the index for all items less food and energy remained at
1.7 percent for the fifth month in a row. The energy index rose 10.1 percent
over the past 12 months, its largest 12-month increase since the period ending
March 2017. The food index increased 1.2 percent over the last year.
Hurricane Irma had a small impact on data collection in September. Data collection
was affected in some areas in Florida.
Table A. Percent changes in CPI for All Urban Consumers (CPI-U): U.S. city average
Seasonally adjusted changes from
Mar. Apr. May June July Aug. Sep. ended
2017 2017 2017 2017 2017 2017 2017 Sep.
All items.................. -.3 .2 -.1 .0 .1 .4 .5 2.2
Food...................... .3 .2 .2 .0 .2 .1 .1 1.2
Food at home............. .5 .2 .1 -.1 .2 -.2 .0 .4
Food away from home (1).. .2 .2 .2 .0 .2 .3 .3 2.4
Energy.................... -3.2 1.1 -2.7 -1.6 -.1 2.8 6.1 10.1
Energy commodities....... -6.0 1.3 -6.2 -2.7 .0 6.1 12.6 18.9
Gasoline (all types).... -6.2 1.2 -6.4 -2.8 .0 6.3 13.1 19.3
Fuel oil (1)............ -.8 -.3 -2.8 -3.7 -2.0 2.9 8.2 15.6
Energy services.......... -.3 .9 .7 -.5 -.2 -.1 -.2 2.2
Electricity............. -.1 .6 .3 -.6 .4 .0 .0 1.7
Utility (piped) gas
service.............. -.8 2.2 1.9 -.2 -2.3 -.5 -.8 3.8
All items less food and
energy................. -.1 .1 .1 .1 .1 .2 .1 1.7
Commodities less food and
energy commodities.... -.3 -.2 -.3 -.1 -.1 -.1 -.2 -1.0
New vehicles............ -.3 -.2 -.2 -.3 -.5 .0 -.4 -1.0
Used cars and trucks.... -.9 -.5 -.2 -.7 -.5 -.2 -.2 -3.7
Apparel................. -.7 -.3 -.8 -.1 .3 .1 -.1 -.2
Medical care commodities .2 -.8 .4 .7 1.0 -.1 -.8 1.0
Services less energy
services.............. -.1 .1 .2 .2 .2 .4 .2 2.6
Shelter................. .1 .3 .2 .2 .1 .5 .3 3.2
Transportation services .4 -.2 .3 .2 .2 .4 .3 3.9
Medical care services... .1 .0 -.1 .3 .3 .2 .1 1.7
1 Not seasonally adjusted.
The food index rose 0.1 percent in September, the same increase as in August. The
index for food away from home rose 0.3 percent, while the index for food at home
was unchanged in September after declining in August. Among the six major grocery
store food group indexes, there were three increases and three declines. The index
for nonalcoholic beverages increased 0.4 percent after falling 0.4 percent in
August. The indexes for cereals and bakery products and for other food at home
also increased in September.
The index for dairy and related products fell 0.6 percent in September following a
0.4-percent decline in August. The index for meats, poultry, fish and eggs also
continued to fall, declining 0.4 percent. The index for fruits and vegetables fell
0.2 percent, with the fresh vegetables index declining 0.8 percent, but the index
for fresh fruits rising 0.5 percent.
Over the last 12 months, the index for food at home rose 0.4 percent. The index
for fruits and vegetables rose 1.2 percent over the span, the largest increase
among the major grocery store food groups. The indexes for cereals and bakery
products and for dairy and related products both declined slightly over the last
12 months. The index for food away from home rose 2.4 percent over the last year.
The energy index increased 6.1 percent in September following a 2.8-percent
increase in August. The major factor in the increase was a 13.1-percent rise in
the gasoline index, the largest monthly increase since June 2009. (Before seasonal
adjustment, gasoline prices increased 10.6 percent in September.) The fuel oil
index also rose sharply, increasing 8.2 percent. However, the electricity index
was unchanged and the index for natural gas declined 0.8 percent.
The gasoline index increased 19.3 percent over the last 12 months. The other
energy component indexes also rose over the past year, with the index for natural
gas rising 3.8 percent and the index for electricity increasing 1.7 percent.
All items less food and energy
The index for all items less food and energy increased 0.1 percent in September
following a 0.2-percent rise in August. The shelter index rose 0.3 percent in
September following a 0.5-percent increase in August. The indexes for rent and
owners' equivalent rent both rose 0.2 percent, while the index for lodging away
from home increased 1.5 percent.
The motor vehicle insurance index rose 0.5 percent in September; it has declined
only once in the last 23 months. The education index increased 0.3 percent, and
the index for recreation rose 0.2 percent. The index for wireless telephone
services rose 0.4 percent in September, ending a streak of 14 consecutive
declines. The indexes for alcoholic beverages, personal care, and tobacco also
increased in September.
The index for new vehicles, which was unchanged in August, fell 0.4 percent in
September. The index for household furnishings and operations declined 0.3
percent, and the index for used cars and trucks continued to fall, declining 0.2
percent. The medical care index fell slightly in September, declining 0.1 percent
as declines in the indexes for prescription and nonprescription drugs outweighed
increases in medical care service indexes. The apparel index declined 0.1 percent
The index for all items less food and energy rose 1.7 percent over the past 12
months. The shelter index rose 3.2 percent over that span, and the index for
medical care increased 1.6 percent. The index for new vehicles fell 1.0 percent
over the last 12 months, its largest 12-month decline since the period ending
Not seasonally adjusted CPI measures
The Consumer Price Index for All Urban Consumers (CPI-U) increased 2.2 percent
over the last 12 months to an index level of 246.819 (1982-84=100). For the month,
the index increased 0.5 percent prior to seasonal adjustment.
The Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W)
increased 2.3 percent over the last 12 months to an index level of 240.939
(1982-84=100). For the month, the index increased 0.6 percent prior to seasonal
The Chained Consumer Price Index for All Urban Consumers (C-CPI-U) increased 2.2
percent over the last 12 months. For the month, the index increased 0.6 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 2017 is scheduled to be released on Wednesday,
November 15, 2017, at 8:30 a.m. (EST).
Consumer Price Index Geographic Revision for 2018
In January 2018, BLS will introduce a new geographic area sample for the Consumer
Price Index (CPI). The 2018 revision utilizes the 2010 Decennial Census and
incorporates an updated area sample design, changes the frequency of publication
for several local area indexes, and establishes some new local area and aggregate
indexes. The first indexes using the new structure will be published in February
2018. Additional information on the geographic revision is available at:
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 about 89 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
about 28 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 87 urban areas across the
country from about 6,000 housing units and approximately 24,000 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 87 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
visits or telephone calls 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 27 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
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
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 8.0/225.000 x 100 = 8.0 18.0/110.000 x 100 = 16.4
Use of Seasonally Adjusted and Unadjusted Data
The Consumer Price Index (CPI) 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. For more information on data
revision scheduling, please see the Fact Sheet on Seasonal Adjustment at
https://www.bls.gov/cpi/seasonal-adjustment/questions-and-answers.htm and the Timeline of
Seasonal Adjustment Methodological Changes at
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.
The Bureau of Labor Statistics uses intervention analysis seasonal adjustment 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 in January 2017, BLS adjusted 40 series using intervention
analysis seasonal adjustment, including selected food and beverage items, motor fuels, and
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. In January 2017, revised seasonal factors and seasonally adjusted
indexes for 2012 to 2016 were calculated and published. For series which are directly adjusted
using the Census X-13ARIMA-SEATS seasonal adjustment software, the seasonal factors for 2016 will
be applied to data for 2017 to produce the seasonally adjusted 2017 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. Twenty-seven of the 81 components of the U.S. city average all items index are
not seasonally adjusted for 2017.
For additional information about the CPI visit www.bls.gov/cpi or contact the CPI Information and
Analysis Section at 202-691-7000 or firstname.lastname@example.org.
For additional information on seasonal adjustment in the CPI visit
https://www.bls.gov/cpi/seasonal-adjustment/home.htm or contact the CPI seasonal adjustment section
at 202-691-6968 or email@example.com.
Information from this release will be made available to sensory impaired individuals upon request.
Voice phone: 202-691-5200; Federal Relay Service: 1-800-877-8339.