1

Jonathan C. Weinhagen

weinhagen.jonathan@bls.gov

Jonathan C. Weinhagen is an economist in the 

Office of Prices and Living Conditions, U.S. 

Bureau of Labor Statistics.

Kevin M. Camp

camp.kevin@bls.gov

Kevin M. Camp is an economist in the Office of 

Prices and Living Conditions, U.S. Bureau of 

Labor Statistics.

Comparing NAICS-based Producer Price Index 

industry net output data and International Price 

Program import data

Data users have expressed interest in analyzing trends in 

prices for domestically produced products versus imports 

by comparing Bureau of Labor Statistics (BLS) producer 

price indexes (PPIs) to BLS import price indexes 

(MPIs). Because BLS publishes both PPIs and MPIs 

classified according to the North American Industry 

Classification System (NAICS), potential exists for 

comparing price trends using NAICS-based PPIs and MPIs. 

There are, however, four important potential differences 

between PPIs and MPIs that data users should consider 

before comparing the two series. This article explains these 

potential differences and presents a new data table for 

assessing the comparability of NAICS-based PPIs and 

MPIs. 

Data users have expressed interest in comparing trends in 

prices for domestically produced products versus imports 

using U.S. Bureau of Labor Statistics (BLS) data. BLS 

publishes both producer price indexes (PPIs) and import 

price indexes (MPIs) classified according to the North 

American Industry Classification System (NAICS).1 NAICSbased PPIs measure price change for the domestically 

produced net output of specific industries or industry 

groups, while NAICS-based MPIs measure price change for 

imports to the United States produced by foreign firms.2

Because both PPIs and MPIs use the NAICS-based 

classification system, the potential exists for comparing 

price trends for domestically produced products using PPIs and imported products using MPIs. However, four 

potential differences between PPIs and MPIs must be considered before one compares the two series. In some 

cases, these differences could make comparisons between PPIs and MPIs inappropriate. This article explains 

these potential differences and presents a new data table to help data users assess the comparability of industryMarch 2018
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based PPIs and MPIs. The table could also be used to explain limitations caused by differences in measurement 

objectives and composition when data users compare PPIs and MPIs.

The article begins by explaining potential differences that data users should be aware of when comparing PPIs 

with MPIs. The next section introduces a new data table that they can use to help determine comparability 

between PPIs and MPIs at the 4- and 5-digit NAICS levels. We then provide examples that compare PPIs and 

MPIs for three different industry groups. The examples present issues associated with comparing the two series 

and highlight how users of BLS data can use the new data table to evaluate the comparability of PPIs and MPIs.

Differences between PPI and MPI NAICS data

There are four important potential sources of differences between PPIs and MPIs that should be considered before 

these indexes are used to compare domestic and imported price trends. In general, these differences relate to 

index methodology, relative-importance values, net weighting, and sample compositions. This section describes 

these potential sources of differences.

Primary, secondary, and miscellaneous production

As many as three kinds of production may exist within an industry. Every industry produces primary products, 

which are products made mainly, but not necessarily exclusively, by that industry. In addition, some industries 

produce secondary products or miscellaneous receipts, which are goods or services made chiefly by some other 

industry.

PPI industry net-output indexes measure price changes for the total production of domestic industries including 

primary products, secondary products, and miscellaneous receipts. The PPI can capture these detailed data 

through industry-level sampling and through direct consultation with establishments included in the PPI survey. 

MPIs measure price changes for imports of primary products of industries using directly collected establishment 

data; MPIs exclude prices for secondary products and miscellaneous receipts produced within the industry. The 

MPI sample is selected from the U.S. Customs and Census Bureau trade frame on a product-level basis, and 

products are categorized into the NAICS industry in which they are classified as primary, regardless of the industry 

in which they were produced.3 NAICS-based MPIs are therefore designed to measure price changes only for 

primary products produced abroad and imported by a given industry or industry group.

Among industries in which secondary production or miscellaneous receipts make up a large share of domestic 

production, comparisons between PPIs and MPIs may be less valid. By definition, products included in the 

secondary product and miscellaneous receipts categories of a PPI are not comparable to those included in an 

MPI, which only includes primary products.

Relative importance of industries within industry groups

Within the NAICS structure, the broadest level of aggregation is the 2-digit sector level. Progressively narrower 

groupings of industries are represented by increasingly longer codes. Six-digit codes are used to identify individual 

industries, while 2- through 5-digit codes are used to identify industry groups. NAICS-based import indexes are 

published at 5-digit and higher levels of aggregation. NAICS-based PPIs are published for 6-digit industries and 

higher levels of aggregation. Consequently, comparisons between MPIs and PPIs can only be made at levels of 
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aggregation above the 6-digit industry level. Most 2-, 3-, 4-, and 5-digit NAICS within mining and manufacturing 

have PPI and MPI counterparts.

When comparing PPIs and MPIs for higher-level NAICS categories, an important point to consider is the relative 

importance of industries included in the NAICS category.4 A relative importance shows the percentage an industry 

constitutes of the overall aggregate NAICS category at a specific point in time. Within an aggregate NAICS index 

composed of industries 1 through n, an industry’s relative importance for month c is calculated using the following 

formula:

RIi,c,a = [( i,c,a / i,b,a * Wi,b,a) / i,c,a / i,b,a * Wi,b,a)] * 100,

where

RIi,c,a is the relative importance of industry i in period c to aggregate index a,

i,c,a is the index value for industry i in period c included in aggregate index a,

i,b,a is the index value for industry i in the base period b included in aggregate index a, and

Wi,b,a is the weight for industry i in the base period b within aggregate index a.

5

As the formula shows, relative-importance values are affected by both weights and index changes. Accordingly, if a 

component index increases at a faster rate than other component indexes from the base period to the current 

period, that component’s relative importance will increase relative to the other components.

Comparing PPIs and MPIs for aggregate NAICS categories tends to be problematic if the relative-importance 

values of industries within the NAICS category are substantially different for the PPI and the MPI. In such 

instances, the compositions of the indexes themselves likely differ, causing some users to deem the indexes 

incomparable.

Net-output weights

In compiling price indexes for 6-digit NAICS industries as well as for aggregate industry groups, the PPI program 

uses net weights. Net weights exclude the value of transactions for products produced and sold within an industry 

or industry group. Net weights are constructed by multiplying gross weights (which include intra-industry 

transactions) by net-output ratios. A net-output ratio measures the proportion of the value of a product an industry 

or industry group does not consume and is calculated using the following formula:

NORc,i = 1 − (Usec,i / c,i),

where

NORc,i is the net-output ratio for commodity c produced by industry or industry group i

 ,

Usec,i refers to the use of commodity c by industry or industry group i, and

c,i is the total use of commodity c by all 1-through-n industries.
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The purpose of net weighting is to eliminate multiple counting of price changes from PPIs. In industry-based output 

price indexes, multiple counting occurs when a price index contains prices for industry net output as well as prices 

for inputs used to produce the output. In such cases, a change in the input price could potentially be counted twice 

in the index: first as a change in the price of the input commodity and second as a change in the price of the output 

commodity (resulting from the change in the input price).6

In contrast to PPIs, MPIs do not use net weights. With MPIs, multiple counting is not a concern because all output 

is sold by foreign firms to domestic buyers. Thus all items are, in effect, net outputs. For this reason, it is not 

necessary to construct MPIs using net weights, and there is no multiple counting in the gross-weighted indexes.

Because net weights are used to construct PPIs but not MPIs, PPIs and MPIs could differ even in cases in which 

the composition of the two indexes is very similar on a gross-weighted basis. In instances in which PPI net 

weighting leads to substantial differences between PPI and MPI weights, comparisons of price movements 

between PPIs and MPIs could be problematic because the composition of indexes is different.

Within 6-digit NAICS product mix

In some instances, higher level PPIs and MPIs appear comparable because of the PPI’s percent primary 

production, industry relative-importance values, and the net-output ratios employed by PPI. Nonetheless, they still 

may be incomparable because of differences in the mix of products included in the PPI versus MPI lower level 6-

digit industry indexes.7 For example, both the PPI and MPI for NAICS 334111 measure price changes for the 

output of computer equipment manufacturing. However, the products included in the PPI and MPI could differ 

substantially if the output produced domestically by NAICS 334111 differs from that imported by the same 

industry. The PPI might, for example, consist mostly of laptop computers, whereas the MPI may include 

tablets and notebook computers in addition to laptops. Unfortunately, because the publication of the items 

that compose the PPI and MPI is restricted to protect the confidentiality of surveyed companies, determining 

industry product composition for these indexes is difficult. Usually, data users will need to rely on sources 

outside BLS (if any can be found) to find additional information about domestic versus imported industry 

product mixes.8

Summary

This section described four potential differences that affect comparisons of PPIs and MPIs for NAICS categories. 

Often, these differences can be attributed to production patterns of domestic producers versus producers of U.S. 

imports, or are the result of trade patterns. For example, different relative levels of domestic and foreign production 

by industries within an aggregate NAICS category could cause PPI and MPI industry relative-importance values to 

differ for that NAICS category. Regarding trade patterns, foreign and domestic firms within an industry may 

produce a similar set of products, but the foreign firms may only export a subset of these products to the United 

States, causing the compositions of the PPI and MPI for the industry to differ. In other cases, such as the percent 

primary versus secondary and miscellaneous production, differences between PPI and MPI data result from 

methodological differences between the two indexes. Regardless of the cause, in instances in which differences 

between PPIs and MPIs are relatively large, comparisons of domestic to imported price trends become less 

reliable.

A new table for comparing PPI industry net-output price indexes to 

MPIs
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In March 2018, BLS began publishing a table of information that can be used to help determine the comparability 

of PPIs and MPIs for 4- and 5-digit NAICS categories. (The table also includes information about 6-digit NAICS 

industries because they are the building blocks for 4- and 5-digit NAICS-based PPIs and MPIs and can therefore 

be used to understand the composition of these higher level NAICS indexes). This table is available at https://

www.bls.gov/ppi/comparability-of-ppi-and-mpi.htm and will be updated periodically. The table assists data users in 

determining comparability between PPIs and MPIs by providing data on three of the four areas of potential 

differences addressed above. An excerpt of the table is shown below.

The first column provides the title of the industry or industry group included in the table. The second column 

specifies NAICS industry codes for the data. In column two, 4- and 5-digit industry groups are followed by a set of 

one or more 6-digit industries. The set of industries directly following an industry group shows those included in the 

group. The third and fourth columns provide the relative-importance values of industries to the 4- or 5-digit MPI 

and PPI industry groups, respectively. For example, table 1 shows that in December 2016, soft drink 

manufacturing accounted for 11.59 percent of the MPI for beverage manufacturing and 48.13 percent of the PPI 

for beverage manufacturing. The fifth column provides the net-output ratios the PPI program applies to each 

industry’s weight when constructing 4- or 5-digit PPI industry group indexes. The PPI relative-importance values 

included in this table are based on net weights. Net-output ratios are therefore reflected in the PPI relativeimportance values. The main use of net-output ratios in this table is to help determine whether net weighting is the 

cause of differences between the PPI and MPI relative-importance values or whether differences are due to other 

causes. For example, the table shows that NAICS 327212 (other pressed and blown glass and glassware 

manufacturing) makes up a relatively larger share of NAICS 3272 (glass and glass product manufacturing) in the 

MPI than the PPI. The PPI applies a net-output ratio of 0.926 to all industries included in glass and glass product 

manufacturing. The difference in PPI versus MPI industry relative-importance values for NAICS 3272 is 

consequently not the result of PPI net-output ratios and must be due to other factors. The final column provides the 

percentage of primary production for each 4- and 5-digit NAICS-based PPI. For example, 81.94 percent of the PPI 

for NAICS 3341 is primary production. The remaining 18.06 percent of the index consists of secondary or 

miscellaneous production and, as discussed earlier, consists of products that are not comparable with those in the 

corresponding MPI category.

Industry

NAICS 

code

Import Price Index relative 

importance

Producer Price Index

Relative 

importance

Net-output 

ratio

Percent 

primary

Beverage manufacturing 3121 100.00 100.00 — 94.52

Soft drink manufacturing 312111 11.59 48.13 0.9763 —

Bottled water manufacturing 312112 1.30 3.83 0.9763 —

Ice manufacturing 312113 0.60 0.97 0.9763 —

Breweries 312120 22.58 26.96 0.9976 —

Wineries 312130 33.47 12.79 0.9771 —

Distilleries 312140 30.47 7.32 0.9396 —

Glass and glass product 

manufacturing 3272 100.00 100.00 — 93.95

Table 1. Producer Price Index and Import Price Index comparability statistics, December 2016

See footnotes at end of table.
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•

•

•

Note: NAICS = North American Industry Classification System.

Source: U.S. Bureau of Labor Statistics.

Examples of PPI-to-MPI comparisons

This section provides three examples of how users might use the new information in the comparability statistics 

table when making potential comparisons between PPI and MPI NAICS-based data. Although the new table is 

intended to provide users with information that facilitates analysis of PPI and MPI comparisons, determining the 

level of comparability necessary to make valid comparisons is subjective and remains the responsibility of the user. 

The examples provide some suggestions for users who are considering making comparisons between two sets of 

indexes that have different measurement objectives.

Semiconductors and other electronic equipment manufacturing (NAICS 3344)

The NAICS 3344 industry group includes establishments primarily engaged in manufacturing semiconductors and 

other components for electronic applications. The group contains the following six industries:

NAICS 334412 — bare printed circuit board manufacturing;

NAICS 334413 — semiconductor and related device manufacturing;

NAICS 334416 — capacitor, resistor, coil, transformer, and other inductor manufacturing;

Industry

NAICS 

code

Import Price Index relative 

importance

Producer Price Index

Relative 

importance

Net-output 

ratio

Percent 

primary

Flat glass manufacturing 327211 18.54 13.09 0.926 —

Other pressed and blown 

glass and glassware 

manufacturing

327212 33.44 17.12 0.926 —

Glass container 

manufacturing 327213 23.51 21.78 0.926 —

Glass product manufacturing 

made of purchased glass 327215 24.50 48.01 0.926 —

Millwork 32191 100.00 100.00 — 91.16

Wood window and door 

manufacturing 321911 27.62 53.24 0.9584 —

Cut stock, resawing lumber, 

and planing 321912 0.00 21.29 0.9584 —

Other millwork (including 

flooring) 321918 72.38 25.47 0.9584 —

Computer and peripheral equipment 

manufacturing 3341 100.00 100.00 — 81.94

Electronic computer 

manufacturing 334111 56.55 55.46 0.9739 —

Computer storage device 

manufacturing 334112 10.50 11.47 0.6527 —

Other electronic component 

manufacturing 334118 32.95 33.06 0.9463 —

Table 1. Producer Price Index and Import Price Index comparability statistics, December 2016
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•

•

•

NAICS 334417 — electronic connector manufacturing;

NAICS 334418 — printed circuit assembly, electronic assembly, manufacturing; and

NAICS 334419 — other electronic component manufacturing.

For analysis purposes, table 2 is an excerpt for NAICS 3344 from the overall PPI–IPP comparison table.

A comparison of December 2016 6-digit PPI and MPI industry relative-importance values for NAICS 3344 implies 

that, on an industry-by-industry basis, the components of the PPI and MPI are fairly similar. For both the PPI and 

MPI, the semiconductor and related device manufacturing industry accounts for the largest share of the overall 

industry group. The share is larger for the MPI than PPI, with semiconductor and related device manufacturing 

accounting for approximately 59 percent of the MPI and 48 percent of the PPI. For both the PPI and MPI, the 

printed circuit assembly manufacturing industry makes up the second largest share of the overall category, 

accounting for about 21 percent of the MPI and 23 percent of the PPI. The industry for other electronic component 

manufacturing composes about 12 percent of the PPI and 6 percent of the MPI, and for both is the third largest 

industry included in the overall category. An analysis of relative-importance values shows that the industry 

composition of the PPI and MPI for NAICS 3344 is similar enough not to disqualify comparisons of the PPI and 

MPI. However, keeping relative-importance differences in mind is still important when comparing PPI data with MPI 

data for NAICS 3344.

Users may also want to consider how PPI net-output ratios affected the relative-importance values. The net-output 

ratios PPI applies to individual industry weights when compiling the net-output price index for NAICS 3344 are all 

similar, ranging from 0.8731 to 0.9290. Such differences in PPI industry net-output ratios are too small to 

contribute to any of the larger differences in relative-importance values between the PPI and MPI. Instead, relativeimportance differences must be the result of differing production or trade patterns and price movements between 

foreign versus domestic producers within NAICS 3344.

Finally, table 2 shows that primary production accounts for approximately 91 percent of the PPI for NAICS 3344, 

implying that secondary and miscellaneous production together account for around 9 percent of the overall index. 

Therefore, a reasonable conclusion is that a secondary and miscellaneous production level of 9 percent is not high 

enough to deem the PPI and MPI incomparable.

Industry

NAICS 

code

Import Price Index relative 

importance

Producer Price Index

Relative 

importance

Net-output 

ratio

Percent 

primary

Semiconductor and other electronic 

component manufacturing 3344 100.00 100.00 — 90.65

Bare printed circuit board 

manufacturing 334412 3.04 7.93 0.8731 —

Semiconductor and related device 

manufacturing 334413 58.56 47.76 0.9290 —

Table 2. Producer Price Index–Import Price Index comparability statistics for semiconductor and other 

electronic equipment manufacturing, December 2016

See footnotes at end of table.
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Note: NAICS = North American Industry Classification System.

(1) For this industry, the Producer Price Index (PPI) coding differs from NAICS. The PPI code for this index is 33441K.

Source: U.S. Bureau of Labor Statistics.

Figure 1 presents the PPI and MPI for NAICS 3344 (semiconductor and other electronic component 

manufacturing) from January 2006 through March 2017. Over that period, prices received by domestic producers 

of semiconductor and other electronic components fell 23.2 percent, and prices for imports decreased 23.3 

percent. It is important to note that the data cannot show whether the absolute price level of imported 

semiconductors and other electronic components is lower or higher than those produced domestically. When data 

users compare PPIs and MPIs, no inferences can be made about differences or similarities in absolute price levels 

of domestically produced versus foreign-produced products. PPIs and MPIs can only be used to assess relative 

price trends in domestic versus foreign goods. Despite that limitation, analysis of PPI and MPI data does reveal 

that price trends of foreign and domestic producers within NAICS 3344 (semiconductors and other electronic 

components) have been similar over the last 12 years.

Industry

NAICS 

code

Import Price Index relative 

importance

Producer Price Index

Relative 

importance

Net-output 

ratio

Percent 

primary

Capacitor, resistor, coil, 

transformer, and other inductor 

manufacturing

334416(1) 6.39 3.69 0.8731 —

Electronic connector 

manufacturing 334417 5.17 5.18 0.8731 —

Printed circuit assembly 

(electronic assembly) 

manufacturing

334418 20.75 23.30 0.8774 —

Other electronic component 

manufacturing 334419 6.08 12.14 0.8731 —

Table 2. Producer Price Index–Import Price Index comparability statistics for semiconductor and other 

electronic equipment manufacturing, December 2016
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•

•

•

Communications equipment manufacturing (NAICS 3342)

The NAICS 3342 industry group consists of establishments primarily engaged in manufacturing wired telephone 

and data communications equipment, radio and television broadcast and wireless communications equipment, and 

all other communications equipment. NAICS 3342 includes these three 6-digit industries:

NAICS 334210 — telephone apparatus manufacturing,

NAICS 334220 — radio and TV broadcast and wireless equipment manufacturing, and

NAICS 334290 — other communications equipment manufacturing.

Table 3 is an excerpt of the NAICS 3342 portion of the overall PPI–IPP comparison table.

Industry

NAICS 

code

Import Price Index relative 

importance

Producer Price Index

Relative 

importance

Net-output 

ratio

Percent 

primary

Communications equipment 

manufacturing 3342 100.00 100.00 — 85.01

Table 3. Producer Price Index–Import Price Index comparability statistics for communication equipment 

manufacturing, December 2016

See footnotes at end of table.
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Note: NAICS = North American Industry Classification System.

Source: U.S. Bureau of Labor Statistics.

Relative-importance values of the 6-digit industries included in the PPI and MPI for NAICS 3342 suggest 

significant compositional differences between the PPI and MPI for communications equipment manufacturing. The 

MPI is made up almost entirely of the industry for radio and TV broadcast and wireless equipment manufacturing. 

The industry for radio and TV broadcast and wireless equipment manufacturing also makes up a large share of the 

PPI; however, the more-than-61-percent share is substantially lower than that of the MPI. The industry for 

telephone apparatus manufacturing accounts for about 30 percent of the PPI but only less than 2 percent of the 

MPI. Finally, the industry for other communications equipment manufacturing makes up close to 9 percent of the 

PPI but less than 2 percent of the MPI. Analysis of industry relative-importance values for NAICS 3344 suggests 

that compositional differences between the two series likely make comparisons between the indexes problematic.

Looking at table 3, we see that primary production accounts for about 85 percent of the PPI for NAICS 3342, and 

the remaining 15 percent is secondary production and miscellaneous receipts. The relatively high level of 

secondary and miscellaneous production within the PPI indicates that comparing domestic versus imported price 

trends for communication equipment may not be possible with PPI and MPI data. Further complicating the 

comparison is that the products manufactured by the industry for radio and TV broadcast and wireless equipment 

likely differ between domestic producers and foreign importers. Products manufactured by this industry include 

transmitting and receiving antennas, cable television equipment, GPS equipment, pagers, cellular phones, mobile 

communications equipment, and radio and television studio and broadcasting equipment. The items included in 

the MPI for radio and TV broadcast and wireless equipment manufacturing (which accounts for almost all of the 

MPI for NAICS 3342) likely differ substantially from those included in the PPI for the same industry because the 

United States is a heavy importer but not producer of cell phones.

Figure 2 shows the PPI and MPI for communications equipment manufacturing from January 2006 to March 2017. 

Over the period, the PPI and MPI showed substantially different movements, with the PPI edging down 1.7 percent 

and the MPI dropping 18.5 percent. However, on the basis of the earlier analysis, conclusions about similarities or 

differences in domestic versus imported communications equipment price trends using PPI and MPI data are 

problematic because the indexes are not comparable in composition.9

Industry

NAICS 

code

Import Price Index relative 

importance

Producer Price Index

Relative 

importance

Net-output 

ratio

Percent 

primary

Telephone apparatus 

manufacturing 334210 1.90 29.77 0.9776 —

Radio and television 

broadcasting and wireless 

communications equipment 

manufacturing

334220 96.37 61.49 0.9174 —

Other communications 

equipment manufacturing 334290 1.73 8.75 0.9923 —

Table 3. Producer Price Index–Import Price Index comparability statistics for communication equipment 

manufacturing, December 2016
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•

•

•

•

•

•

•

Basic chemical manufacturing (NAICS 3251)

Establishments in industry group NAICS 3251 primarily manufacture basic chemicals. The grouping includes the 

following seven industries:

NAICS 325110 — petrochemical manufacturing,

NAICS 325120 — industrial gas manufacturing,

NAICS 325130 — synthetic organic dye and pigment manufacturing,

NAICS 325180 — other basic inorganic chemical manufacturing,

NAICS 325193 — ethyl alcohol manufacturing,

NAICS 325194 — gum and wood chemical manufacturing, and

NAICS 325199 — all other basic organic chemical manufacturing.

Table 4 is an excerpt from the PPI–IPP comparison table describing NAICS 3251.
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Note: NAICS = North American Industry Classification System.

Source: U.S. Bureau of Labor Statistics.

An analysis of the relative-importance values of basic chemical manufacturing industries suggests that, although 

the PPI and MPI have similarities, there are some differences between the indexes. For both the PPI and MPI, the 

industry for all other basic organic chemical manufacturing is the most important component. All other basic 

organic chemical manufacturing accounts for about 60 percent of the MPI and 45 percent of the PPI. The second 

largest component in both, accounting for roughly 22 percent of the MPI and PPI, is other basic inorganic chemical 

manufacturing. The industry for petrochemical manufacturing is the third largest component for PPI, accounting for 

about 14 percent of the overall grouping with a net-output ratio of 0.4874 but only accounts for around 4 percent of 

the MPI for basic chemical manufacturing. Within the MPI, the third most important component is gum and wood 

chemical manufacturing. When we take relative-importance values into account, we find that the comparability of 

the PPI and MPI for basic chemical manufacturing is ambiguous.

Additional differences, however, should be considered when users compare the data. The PPI for basic chemical 

manufacturing is made up of about 79 percent primary production and 21 percent secondary production and 

miscellaneous receipts. Consequently, about 21 percent of the PPI and MPI composition necessarily differ, which 

further reduces the comparability of the PPI and MPI for NAICS 3251.

Overall, the comparability of the PPI and MPI for basic chemical manufacturing is unclear. There are differences 

based on relative-importance values as well as the percentage of secondary products and miscellaneous receipts 

included in the PPI. However, despite these differences, most of the industries in NAICS 3251 produce products 

that largely come from fuel feedstocks. Therefore, there is a reasonable expectation that the indexes should have 

similar trends.

Industry

NAICS 

code

Import Price Index relative 

importance

Producer Price Index

Relative 

importance

Net-output 

ratio

Percent 

primary

Basic chemical manufacturing 3251 100.00 100.00 — 78.84

Petrochemical 

manufacturing 325110 3.73 14.38 0.4874 —

Industrial gas 

manufacturing 325120 0.37 5.62 0.8926 —

Synthetic organic dye and 

pigment manufacturing 325130 5.22 3.69 0.9605 —

Other basic inorganic 

chemical manufacturing 325180 22.48 22.22 0.8969 —

Ethyl alcohol 

manufacturing 325193 1.03 5.95 0.8263 —

Gum and wood chemical 

manufacturing 325194 7.49 3.61 0.8263 —

All other basic organic 

chemical manufacturing 325199 59.69 44.53 0.8263 —

Table 4. Producer Price Index–Import Price Index comparability statistics for basic chemical 

manufacturing, December 2016
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Looking at figure 3, we see that the PPI for basic chemicals rose 26.3 percent from January 2006 to March 2017. 

During the same period, prices for imports rose 38.2 percent. Despite the overall higher rate of increase in the 

MPI, the PPI and MPI trends were similar over most of the sample period. The main exception was from 2006 

through early 2007, when the MPI increased and the PPI showed little change.

Conclusion

This article examined the potential of using PPI net-output indexes and MPIs to compare price trends in 

domestically produced and imported products. The article began by explaining four potential sources of differences 

between PPIs and MPIs that data users should consider before comparing domestic and imported price trends.

A new Producer Price Index–Import Price Index comparability statistics table providing data on three of the four 

areas of potential differences between PPI and MPI was also presented. The purpose of this table is to assist data 

users to make informed decisions regarding the comparability of PPI and MPI NAICS-based industry group price 

indexes. This table can be found at https://www.bls.gov/ppi/comparability-of-ppi-and-mpi.htm. Although the new 

tables and the examples within this article help to provide users with the information necessary to facilitate the 

analysis of PPI and MPI comparisons, determining the level of comparability necessary to make valid comparisons 

is subjective and the responsibility of the data user. Users should also keep in mind that even though many index 

comparisons match on the basis of relative importance values, NORs, and percent primary, differences in product 

mixes may still make comparisons problematic. Ultimately, all measures should be looked at in combination with 
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industry product composition as well as knowledge about general industry market conditions before final decisions 

on comparability are made.

SUGGESTED CITATION

Jonathan C. Weinhagen and Kevin M. Camp, "Comparing NAICS-based Producer Price Index industry net output 

data and International Price Program import data," Monthly Labor Review, U.S. Bureau of Labor Statistics, March 

2018, https://doi.org/10.21916/mlr.2018.7

NOTES

1 NAICS uses a production-oriented conceptual framework to group establishments into industries on the basis of the primary activity 

in which they are engaged. Establishments using similar raw materials, capital equipment, and labor are classified in the same 

industry. Additional information can be found at https://www.bls.gov/bls/naics.htm.

2 Methodological information about PPI and MPI can be found at https://www.bls.gov/ppi/methodology.htm and https://www.bls.gov/

mxp/methodology.htm, respectively.

3 The U.S. Customs and Census Bureau trade frame is the dollar value of all goods imported to the United States in a given year. The 

MPI sample is based on a 2-year lag of these data; for example, the 2018 trade frame contains data from 2016.

4 PPI calculates and publishes 6-digit industry indexes, whereas IPP calculates but does not publish 6-digit MPIs. Both programs, 

however, construct industry group indexes by aggregating industry level indexes.

5 MPI weights are based on Census value of imports data, while PPI weights are based on Census domestic value of shipments or 

revenue data. Information currently used to calculate weights throughout the PPI family of indexes is taken largely from the following 

censuses conducted by the Census Bureau of the U.S. Department of Commerce: (1) Census of Manufactures, (2) Census of Mineral 

Industries (which includes oil and gas production), (3) Census of Agriculture, and (4) Census of Service Industries. Other current 

sources of weighting include the Energy Information Administration of the U.S. Department of Energy and the National Marine Fisheries Service of the U.S. Department of Commerce. Weights are updated at approximately 5-year intervals. MPI weights are based on 

trade-value figures compiled by the Bureau of the Census for the base year.

6 The following hypothetical example is provided to further illustrate how PPI calculates net weights. The primary production of the car 

and light truck industries is cars and light trucks, respectively. Both of these industries, however, also produce automobile parts as 

secondary production. The total value of automobile parts produced across all industries is $100,000,000, with car and light truck 

manufacturers producing $1,000,000 and $500,000 of the total, respectively. Of the total $100,000,000 of automobile parts produced, 

car manufacturers consume $40,000,000 and light truck manufacturers consume $30,000,000. The net-output ratio for automobile 

parts for car manufacturers is calculated as follows:

NORauto parts,car mfg = 1 − (Useauto parts,car mfg / auto parts,i)

= 1 – ($40,000,000 / $100,000,000)

= 0.6

This NOR calculation implies that car manufacturers consume 40 percent of automobile parts, and the remaining 60 percent are sold 

to industries other than car manufacturers. The net weight for car parts produced by car manufacturers is calculated by multiplying the 

gross weight by the NOR as follows: net weightauto parts,car mfg = 0.6 * $1,000,000 = $600,000.

NORauto parts,truck mfg = 1 − (Useauto parts,truck mfg / auto parts,i)

= 1 – ($30,000,000 / $100,000,000)

= 0.7
 U.S. BUREAU OF LABOR STATISTICS

15

MONTHLY LABOR REVIEW 

The above calculation shows that truck manufacturers consume 30 percent of automobile parts, and the remaining 70 percent are 

sold to industries other than truck manufacturers. The net weight for car parts produced by truck manufactures is then calculated by 

multiplying the gross weight by the NOR as follows: net weightauto parts, truck mfg = 0.7 * 500,000 = $350,000. The PPI constructs netoutput price indexes through the use of data on detailed industry flows from input–output tables compiled by the Bureau of Economic 

Analysis (BEA) and from other detailed industry data. For additional BEA information, see https://www.bea.gov/industry/

io_benchmark.htm.

7 See endnote 4.

8 Within its NAICS-based industry structure, PPI often publishes data to at least the 7-digit product level. Data users could examine 

this structure to help determine the domestic production of an industry. This type of data, however, is not available for MPIs.

9 Any user attempting to make such a comparison should at least note the significant limitations due to these differences in 

composition.

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