Quarterly Hogs and Pigs - Quality Measures

Quarterly Hogs and Pigs Methodology
and Quality Measures
ISSN: 2166-9813

Released January 24, 2023, by the National Agricultural Statistics Service (NASS), Agricultural Statistics Board, United States Department
of Agriculture (USDA).

Quarterly Hogs and Pigs Survey Methodology
Scope and Purpose: The Hogs and Pigs Survey is conducted quarterly in December, March, June, and September. The
survey targets hog and pig producers in the United States. The survey collects data for total hog inventory and other
components including breeding herd, market hog inventory, market hogs by weight group, farrowings, pig crop, and litter
rate. Additional data is collected for death loss, on-farm and custom slaughter, inventory values, and hogs raised under
contract. Data is published for 16 major states every quarter except December when every state is published.
Survey Timeline: The reference date for the Hogs and Pigs Survey is the first day of the quarterly month with a data
collection period of 15 days. Regional Field Offices (RFO) may begin data collection one day prior to the reference date.
Data collection continues until a scheduled ending date, and RFO have about four or five business days to complete
editing and analysis, execute the summary, and interpret the survey results. The Agricultural Statistics Board (ASB) must
perform the National review, reconcile State estimates to the National estimates, and prepare the official estimates for
release in five or six business days. The estimates are usually released to the public by the last week in the quarterly
month. The publication date may change due to the timing of federal holidays.
Sampling: The target population for the Hogs and Pigs Survey is all agricultural establishments with one or more hogs or
pigs owned by the operation. NASS uses a dual frame approach, consisting of list frame and area frame components, to
provide complete coverage of this target population. The Hogs and Pigs Survey is conducted for every state.
The list frame includes all known agricultural establishments. Livestock inventory of each establishment is maintained on
the list frame to allow NASS to define list frame sampling populations for specific surveys and to employ efficient
sampling designs. Only list frame records with recent positive hog inventory data are included in the list frame population.
In December, a base sample is selected for all states in the survey. During the follow-on quarters, the list sample is split
into five replicates and only a partial number of replicates are contacted. This is done to reduce the burden of multiple
survey contacts on the respondents in one calendar year. The list frame hog population covers approximately 99 percent of
hog inventory in the United States.
The area frame contains all land in the state and, as such, is complete. The land is stratified according to intensity of
agriculture using satellite imagery. The land in each stratum is divided into segments of roughly one square mile.
Segments are optimally allocated and sampled to effectively measure crops and livestock. The sampled segments are fully
enumerated in June. All farms and ranches found operating tracts in these segments are checked to see if they are included
in the list frame hog population. The farms and ranches that are not included in the list frame hog population, called
nonoverlap tracts, are sampled for the December Hogs and Pigs Survey so that the target population is completely
represented. The area frame component of the December Hogs and Pigs Survey covers approximately one percent of the
December hog inventory in the United States. The area frame component is modeled for the other three quarters to reduce
respondent burden.
The Hogs and Pigs Survey list frame sample is selected using a hierarchical stratified sampling design with strata defined
by total hogs and pigs. The sample is a panel sample and is designed to achieve a standard error of one percent of the
point estimate for total hogs and pigs at a National level. The Hogs and Pigs Survey nonoverlap sample uses a stratified
sample design based on data collected in the June Area Frame Survey. Each list frame and area frame sampling unit are
assigned a sampling weight which is used to create the survey estimates.

Data Collection and Editing: For consistency across modes, the paper version is considered the master questionnaire and
the Computer Assisted Telephone Interview (CATI), Computed Assisted Self Interview (CASI), and Mobile Computer
Assisted Personal Interview (mCAPI) instruments are built to model the paper instrument. Questionnaire content and
format are evaluated annually through a specifications process where requests for changes are evaluated and approved or
disapproved. Input may vary from question wording or formatting to a program change involving the deletion or
modification of current questions or addition of new ones. If there are significant changes to either the content or format
proposed, a NASS survey methodologist will pre-test the changes for usability. Prior to the start of data collection, all
modes of instruments are reviewed and the paper, mCAPI, CASI and CATI instruments are thoroughly tested.
All federal data collections require approval by the Office of Management and Budget (OMB). NASS must document the
public need for the data, apply sound statistical practice, prove the data does not already exist elsewhere, and ensure the
public is not excessively burdened. The questionnaire must display an active OMB number that gives NASS the authority
to conduct the survey, a statement of the purpose of the survey and the use of the data being collected, a response burden
statement that gives an estimate of the time required to complete the form, a confidentiality statement that the
respondent’s information will only be used for statistical purposes in combination with other producers, and a statement
saying that response to the survey is voluntary and not required by law.
In addition to asking the specific hog inventory items, all instruments collect information to verify the sampled unit,
determine any changes in the name or address, identify any partners to detect possible duplication, verify the farm still
qualifies for the target population, and identify any additional operations operated by the sampled operator.
Sampled farms and ranches receive a pre-survey letter explaining the survey and informing them that they will be
contacted for survey purposes only. The letter provides the questions to be asked to allow respondents to prepare in
advance and also provides a pass code they can use to complete the survey on the internet. All modes of data collection
are utilized for hog surveys. RFOs are given the option of conducting a mail out/mail back phase. While mail is the least
costly mode of collection, the short data collection period and the uncertainty of postal delivery times limit its
effectiveness. Most of the data are collected by computer-assisted telephone interviews (CATI) by RFO and Data
Collection Centers. A program is run to determine if any sampled farms are in multiple on-going surveys, so data
collection can be coordinated.
Survey Edit: As survey data are collected and captured, they are edited for consistency and reasonableness using
automated systems. The edit logic ensures the coding of administrative data follows the methodological rules associated
with the survey design. Relationships between data items on the current survey are verified and in certain situations those
items may be compared to data from earlier surveys to make sure certain relationships are logical. The edit will determine
the status of each record to be either “dirty” or “clean”. Dirty records must be updated and reedited or certified by an
analyst to be clean. If updates are needed, they are reedited interactively. Only clean records are eligible for analysis and
summary.
Analysis Tools: Edited data are processed through an interactive analysis tool which displays data for all reports by item.
The tool provides scatter plots, tables, charts, and special tabulations that allow the analyst to compare an individual
record to other similar records within their state. Outliers and unusual data relationships become evident and RFO staff
will review them to determine if they are correct. The tool also allows comparison to previously reported data to detect
large changes in the operation. Suspect data found to be in error are corrected, while data found to be correct are kept.
Nonsampling Errors: Nonsampling errors are present in any survey process. These errors include reporting, recording,
editing, and imputation errors. Steps are taken to minimize the impact of these errors, such as questionnaire testing,
comprehensive interviewer training, validation and verification of processing systems, detailed computer edits, and the
analysis tool.
Estimators: Each farm and ranch in the sample has an initial sampling weight. This is the inverse of the sampling
fraction. For example, if a stratum has 1,000 farms in the population and 200 are sampled for this survey, each sampled
farm has a weight of 5. In other words, each sampled farm represents 5 farms. The nonoverlap tracts sampled to measure
the hogs and pigs not accounted for by the list have a weight determined by adjusting their original area frame weight by
any second stage sampling weight.
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Quarterly Hogs and Pigs Methodology and Quality Measures (January 2023)
USDA, National Agricultural Statistics Service

Response to the Hogs and Pigs Survey is voluntary. Some producers refuse to participate in the survey. Others cannot be
located during the data collection period, and some submit incomplete reports. These nonrespondents must be accounted
for if accurate estimates of hogs are to be made. For the Hogs and Pigs Survey, most nonrespondents are accounted for by
adjusting the weights of the respondents. The adjustment occurs by stratum as the bounded strata represent homogeneous
groupings of similar sized farms. Also, the adjustment is performed for each individual item (total hogs, market hogs, pig
crop) because sometimes only a partial report is obtained. The largest stratum is unbounded and is made up of large and,
often unique, farms. Nonrespondents in this stratum and the nonoverlap tracts must be manually imputed by RFO
statisticians and their weights are not adjusted.
Two estimators are used to compute direct measures of the hog inventory items. The “reweighted” estimator and the
“adjusted” estimator are computationally identical except in how the nonresponse adjustments are made. The reweighted
estimator uses a global weight adjustment across all reported and estimated reports. Using the previous example, if 180 of
the original 200 respond, the weights of the 180 will be adjusted to 1,000 divided by 180, or 5.56. The nonresponse
weight adjustment for the adjusted estimator uses an additional piece of information. When a sampled farm refuses to
cooperate, interviewers will probe to determine the presence of hogs even though the number is not known. This
presence/absence indicator is used in the weight adjustment.
Point estimates, also called direct expansions, for both estimators are calculated by multiplying the reported value by the
nonresponse weight and summing to a stratum total. A variance estimate is also computed at the stratum level. The
nonoverlap tracts are treated as an additional stratum. Totals and variances are additive across strata to form a State
estimate and states are additive to a National estimate.
Ratio estimates are also computed for many items. For example, market hogs can be estimated as a percent of total
inventory. A matched record ratio of current quarter data to previous quarter data is used to indicate change. Ratio
indications use the reweighted estimator described above for the numerator and denominator. Both the numerator and
denominator must be complete for that record to be included in the ratio estimator.
Estimation: When all samples are accounted for, all responses fully edited, and the analysis material is reviewed, each
RFO executes summaries for their states. When all states have been summarized, Headquarters executes the National
summary. Since all states conduct identical surveys, the samples can be pooled, and National survey results computed.
The summary results provide multiple point estimates and their standard errors for each data series being estimated. It also
provides information used to assess the performance of the current survey and evaluate the quality of the survey estimates,
such as strata level expansions, response rates, and percent of the expansion from usable reports.
RFO are responsible for performing a detailed review of their survey results. Any irregularities revealed by the summary
must be investigated and, if necessary, resolved. Using the historical relationship of the survey estimates to the official
estimate, RFO must interpret the survey results and submit a recommended estimate to Headquarters for all data series for
which they are in the NASS program. The data are viewed in tabular and graphical form and a consensus estimate is
established. RFO see their survey results only and do not have access to other Regions’ results. For some data series,
information from other sources is also utilized in the process of establishing estimates. This includes commercial slaughter
data, imports, and exports.
For the National estimates, NASS assembles a panel of statisticians to serve as the ASB which reviews the National
results and establishes the National estimates. Since larger sample sizes yield more precise results, NASS employs the
“top-down” approach by determining the National estimates first and reconciling the state estimates to the National
number for hog inventory, pig crop, and farrowings. The ASB has the advantage of being able to examine results across
states, compare the state recommendations, and utilize administrative data available only at the United States level. The
same estimators used in the state summaries are produced by the National summary. The ASB follows the same approach
the states do in determining the National estimate. The historical relationship of the survey estimates to the official
estimate is evaluated over time to determine accuracy and bias using tables and graphs. Every five years NASS conducts
the Census of Agriculture, which is an exhaustive data collection effort for all known farm operations across the United
States. The information gathered from the Census of Agriculture is used to establish “benchmark” levels by which the
survey estimators can be compared, and bias determined. Survey based estimators can also be impacted by outliers –
Quarterly Hogs and Pigs Methodology and Quality Measures (January 2023)
USDA, National Agricultural Statistics Service

3

individual reports that have excessive influence on the results due to either improper classification or extremely unusual
data for a given operation (i.e., the operation is not representative of other operations). NASS thoroughly reviews the
survey data to identify these situations and considers their impact on the survey results when establishing the official
estimates.
External information (administrative data) is also utilized in the process of setting estimates. In order to be considered fit
for use, these data must be deemed to be reliable and come from unbiased sources. The most common administrative data
is commercial slaughter. NASS employs a balance sheet approach whenever possible to ensure that estimates are as
accurate as possible. This approach typically is limited to National-level estimates. A balance sheet and its components
are reviewed when the inventory numbers are established. Commercial slaughter is an important element of the balance
sheet at the National level since its high degree of reliability is based on a near-actual count of animals slaughtered. Live
United States imports and exports to other countries are also considered.
Subtracting the disposition components of the balance sheet from supply components should, theoretically, give the
current inventory. However, each component of the balance sheet has varying degrees of possible estimation error. To be
most useful as an indication of inventory, therefore, each component should be estimated based on all available
information. The supply components of the United States balance sheet are the beginning inventory, births, and imports
(inshipments for State balance sheets). From this supply, the disposition components – commercial slaughter (marketings
at State level), farm slaughter, deaths, and exports – are subtracted. The result is the indicated number on hand at the end
of the period or year.

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Quarterly Hogs and Pigs Methodology and Quality Measures (January 2023)
USDA, National Agricultural Statistics Service

Quality Metrics for Hogs and Pigs
Purpose and Definitions: Under the guidance of the Statistical Policy Office of the Office of Management and Budget
(OMB), the United States Department of Agriculture’s National Agricultural Statistics Service (NASS) provides data
users with quality metrics for its published data series. The metrics tables below describe the performance data for all
surveys contributing to the publication. The accuracy of data products may be evaluated through sampling and nonsampling error. The measurement of error due to sampling in the current period is irrelevant for a fully enumerated data
series. Non-sampling error is evaluated by response rates and the weighted item response rates.
Sample size is the number of observations selected from the population to represent a characteristic of the
population. Operations that did not have the item of interest or were out of business at the time of data collection
have been excluded.
Response rate is the proportion of the above sample size that completed the survey.
Weighted item response rate is a ratio of reported survey data expanded by the original sampling weight
compared to final nonresponse adjusted summary totals.
Coefficient of variation provides a measure of the size for the standard error relative to the point estimate and is
used to measure the precision of the results of a survey estimator.
Hogs and Pigs Survey Sample Size and Response Rates: To assist in evaluating the performance of the estimates in the
hogs and pigs report, the sample size and response rates are displayed. Response rates overall for 2021 and 2022 are
displayed.

Hogs and Pigs Survey Sample Size and Response Rates - United States: July 1, 2021-2022
Sample size

Response rates

2021

2022

2021

2022

(number)

(number)

(percent)

(percent)

United States ..........................................................

5,770

5,525

48.4

51.0

Quality Metrics for July 1 Hogs and Pigs – United States: 2021 and 2022
Weighted item
response rate

All hogs and pigs ....................................................
Kept for breeding ................................................
Market ................................................................
Sows farrowed ........................................................
Pig crop ..................................................................

Coefficient
of variation

2021

2022

2021

2022

(percent)

(percent)

(percent)

(percent)

73.8
76.8
73.5
78.1
79.3

Quarterly Hogs and Pigs Methodology and Quality Measures (January 2023)
USDA, National Agricultural Statistics Service

71.9
76.4
71.5
77.4
78.7

0.6
0.6
0.6
0.7
0.7

0.7
0.7
0.7
0.7
0.7

5

Hogs and Pigs Survey Sample Size and Response Rates – United States: 2021 and 2022
Sample size

Weighted item
response rate

Response rate

Coefficient
of variation

2021

2022

2021

2022

2021

2022

2021

2022

(number)

(number)

(percent)

(percent)

(percent)

(percent)

(percent)

(percent)

Alabama ..............................
Alaska ..................................
Arizona ................................
Arkansas ..............................
California .............................
Colorado ..............................
Connecticut ..........................
Delaware .............................
Florida ..................................
Georgia ................................

(D)
21
29
57
67
46
33
26
(D)
36

(D)
18
33
41
56
43
34
26
(D)
61

(D)
57.1
55.2
61.4
32.8
54.3
48.5
15.4
(D)
58.3

(D)
44.4
66.7
56.1
32.1
65.1
35.3
57.7
(D)
37.7

(D)
45.6
99.4
83.7
62.6
79.8
15.3
46.6
(D)
31.9

(D)
67.2
95.5
84.5
61.1
76.7
30.3
69.2
(D)
30.1

(D)
38.8
0.3
1.0
1.1
1.7
38.8
(Z)
(D)
12.9

(D)
(Z)
1.5
2.6
4.3
1.9
9.4
56.5
(D)
14.1

Hawaii ..................................
Idaho ....................................
Illinois ...................................
Indiana .................................
Iowa .....................................
Kansas .................................
Kentucky ..............................
Louisiana .............................
Maine ...................................
Maryland ..............................

39
60
445
427
892
128
60
37
51
39

31
47
415
374
824
136
60
35
52
39

33.3
36.7
43.6
62.3
44.5
31.3
63.3
48.6
39.2
17.9

54.8
55.3
52.3
62.3
48.2
49.3
58.3
57.1
55.8
41.0

30.1
76.0
61.9
51.5
69.3
70.6
75.3
36.3
34.1
10.2

49.4
57.4
67.1
60.6
66.5
81.5
68.9
31.6
45.5
17.7

15.9
3.6
0.9
0.8
1.4
0.7
1.5
31.5
20.8
18.6

7.8
8.4
1.1
1.3
0.9
0.7
10.7
29.7
21.9
14.3

Massachusetts .....................
Michigan ..............................
Minnesota ............................
Mississippi ...........................
Missouri ...............................
Montana ...............................
Nebraska .............................
Nevada ................................
New Hampshire ...................
New Jersey ..........................

46
106
582
37
225
79
406
19
45
31

43
87
562
35
204
82
359
(D)
40
35

52.2
71.7
45.2
48.6
36.4
77.2
48.5
36.8
62.2
38.7

34.9
60.9
46.6
54.3
37.3
70.7
49.9
(D)
65.0
37.1

27.6
74.3
66.1
98.7
81.8
89.0
84.1
3.2
42.3
24.7

34.3
65.7
51.2
96.1
83.6
83.9
82.0
(D)
77.6
33.1

39.1
0.8
2.7
0.3
0.9
0.3
0.8
3.6
25.6
14.6

44.9
3.2
4.9
2.4
1.7
0.4
0.7
(D)
10.2
26.7

New Mexico .........................
New York .............................
North Carolina ......................
North Dakota ........................
Ohio .....................................
Oklahoma ............................
Oregon .................................
Pennsylvania .......................
Rhode Island ........................
South Carolina .....................

24
65
52
63
289
60
58
166
21
45

27
67
48
65
262
68
57
164
17
39

45.8
55.4
76.9
61.9
56.1
28.3
31.0
41.6
23.8
42.2

29.6
41.8
70.8
52.3
58.0
82.4
36.8
46.3
35.3
61.5

38.9
50.4
99.3
81.4
51.4
98.5
11.8
84.4
13.0
95.7

20.9
42.6
98.7
54.6
55.7
98.3
13.0
85.5
(Z)
93.8

25.0
28.2
0.3
0.4
1.0
0.1
23.7
1.0
28.0
1.4

16.9
30.6
0.2
0.3
0.8
0.3
28.3
0.9
(Z)
3.0

South Dakota .......................
Tennessee ...........................
Texas ...................................
Utah .....................................
Vermont ...............................
Virginia .................................
Washington ..........................
West Virginia ........................
Wisconsin ............................
Wyoming ..............................

201
50
82
32
42
36
50
37
209
22

196
48
122
28
56
36
43
49
197
25

46.8
48.0
61.0
84.4
54.8
47.2
40.0
67.6
51.2
59.1

48.5
52.1
69.7
82.1
37.5
33.3
34.9
65.3
48.7
52.0

66.3
93.7
92.2
99.2
15.1
97.6
53.9
49.2
47.9
99.2

65.8
98.1
97.3
99.5
14.8
92.5
38.1
50.9
38.9
98.1

2.1
1.4
3.8
0.1
62.5
0.7
30.5
27.4
8.3
0.5

1.9
0.4
1.5
0.4
48.8
4.5
41.7
36.0
21.7
1.2

Other States 1 ......................

97

139

45.4

41.0

47.4

75.1

21.1

5.9

United States .......................

5,770

5,525

48.4

51.0

73.8

71.9

0.6

0.7

(D) Withheld to avoid disclosing data for individual operations.
(Z) Less than half of the unit shown.
1
Includes data for States not published in this table

6

Quarterly Hogs and Pigs Methodology and Quality Measures (January 2023)
USDA, National Agricultural Statistics Service

Information Contacts
Process
Estimation ....................................
Data Collection ............................
Questionnaires ............................
Sampling and Editing ...................
Summary and Estimators .............
Dissemination ..............................
Media Contact and Webmaster ....

Unit
Livestock Branch
Survey Administration Branch
Data Collection Branch
Sampling Editing and Imputation Methodology Branch
Summary Estimation and Disclosure Methodology Branch
Data Dissemination Office
Public Affairs Office

Telephone
(202) 720-3570
(202) 720-3895
(202) 720-6201
(202) 690-8141
(202) 690-8141
(202) 720-3869
(202) 720-2639

Email
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]

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