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Improvements Of Sample Design For Rural
Statistical Surveys In China
Michael SteinerNational Agricultural Statistics Service
United States Department of Agriculture
Xian ZudeRural Survey Organization
Chinese National Bureau of Statistics
Chinese Census of Agriculture
• First National Agricultural Census --- 1996
• Census Questionnaires – 38 sections, 687 data items
• Data collection – January 1997
• Data collected for approximately 214,000,000 rural households
• Approximately 7,000,000 interviewers were utilized for data collection
Use of Chinese Census Data
• Provides a wealth of crop, livestock and rural household statistics.
• Provides estimates of small administrative units.
• Provides estimates of rare commodities.
• Provides data for a sampling frame.
Chinese Agriculture Statistics
• National Bureau of Statistics (NBS) of PR China
• Food and Agricultural Statistics Centre (FASC) of NBS --- Chinese Census of Agriculture
• Rural Survey Organization (RSO) --- Agricultural & Rural Statistics for China – established in 1984
• Since 1996 --- NBS and the National Agricultural Statistics Service (NASS) of the U.S. Department of Agriculture --- cooperative agreement.
Chinese Survey Program
• Household Survey – farmers income and expenditures – since 1954
• Crop Yield Survey – since 1963
• 857 Sample Counties Were Selected – 1984 • Three types of surveys implemented: * Farmers Household Survey * Crop Yield Survey * Socio-economic Survey
RSO Plan For Survey Expansion
• RSO decided to expand survey program in 1999.
• Expanded survey program to cover: * Crop Area for Major Crops * All Major Types of Livestock (Inventory and Slaughter) * Agricultural Prices and Costs * Poverty Measurement
• Complete Reporting System
Guangdong Province Pilot Survey Work
• Project Involving Guangdong Bureau of Statistics, NBS-RSO, and USDA-NASS
Guangdong Province designated as site for pilot survey work.
• Guangdong Province: * 21 Prefectures * 122 Counties * 23,870 Villages
Objectives
1) Effectively utilize data from the Census of Agriculture
2) To select samples using multiple variables which isnecessary to support the proposed expanded surveyprogram
3) To integrate the statistical needs for different levels ofgovernment
1) Effectively utilize data from the Census of Agriculture
A) Vast amounts of data available from the Census
* Census questionnaire 38 sections 687 items
B) Data available for many administrative areas
* 31 Provinces, Municipalities and Autonomous Regions * 550+ Prefectures and Cities at Prefecture Level * 2,500+ Counties and Cities at County Level * 43,000 Township and Towns * 740,000+ Administrative Villages * 214,000,000 Households
2) To select samples using multiple variables which isnecessary to support the proposed expanded surveyprogram
* Land in farm * Crops * Livestock * Aquaculture * Labor
3) To integrate the statistical needs for differentlevels of government
* National * Provincial * Prefecture * County
Separate samples are now used for each administrative level
Samples are not additive
Census Data Useful For
Analysis
Sampling Alternatives
0
500
1000
1500
2000
Tho
usan
ds
Number of Persons in Rural Households, by County, 1996Guangdong Province
In Sample Not Sample Mean Median
0
100
200
300
400
500
600
700
800
900
1000
Tho
usan
ds
Cultivated Land, by County, 1996Guangdong Province
In Sample Not Sample Mean Median
0
200
400
600
800
1000
1200
Tho
usan
ds
Grain Crops: Area Planted, by County, 1996
In Sample Not Sample Mean Median
Guangdong Province
0
50
100
150
200
250
300
Tho
usan
ds
Vegetables: Area Planted, by County, 1996
Guangdong Province
In Sample Not Sample Mean Median
0
100
200
300
400
500
600
700
Tho
usan
ds
Hog Inventory: Number of Head on Hand, December 31, 1996, by CountyGuangdong Province
In Sample Not Sample Mean Median
Alternative 1
• Select samples from villages within all counties in a province.
Alternative 2
• Select villages within a NEW sample of counties.
• Continue the practice of having samples only in selected counties (not all counties).
• Select a new sample of counties and replace the old sample of counties.
Alternative 3
• Select villages with the current sample of counties.
Using Census Data to Analyze Sampling Strategies
Alternative 1 — Villages within all counties in theprovince.
Alternative 2 — Villages within a new sample ofcounties.
Alternative 3 — Villages within counties currentlyutilized in Rural Household Survey.
Yk,j is the estimate for the jthth replicate and Yk k is the known population total for thesimulated survey response for item.
RMSEk 1000
j 1(Yk,j Yk)2
1000
Comparison of Sample Design Strategies
Ratio of RMSEs (root mean square errors)
Stages of Sampling
Total Area Sown
Total Area for Grain
Total Area for Rice
All Counties, Villages
1 1 1
New Counties, Villages
1.8 3.6 3.1
Old Counties, Villages
5.4 5.6 5.4
Methods of Sampling
Stratified Sampling
***Census Data Available For Stratification***
Disadvantages:
Becomes difficult to create efficient stratified
design when number of variables of interest
increases.
Possible Commodities For Sample Selection
• Land in Grain• Wheat• Rice• Corn• Tuber Crops• Rapeseed• Peanuts• Vegetables
• Orchard Area• Pond Area
• Cattle• Sheep• Hogs• Poultry
Stratified Design ProblemTwo Commodities – Three Size Groupings
ItemsRice Area
(Large)
Rice Area
(Medium)
Rice Area
(Small)
Hog Inventory – Large
L L L M L S
Hog Inventory -Medium
M L M M M S
Hog Inventory
- SmallS L S M S S
MPPS
Methods of Sampling
MPPS Sampling
Multivariate Probability Proportional to Size:
• Probability proportional to size sample design
in which the measure of size is determined
by more than one variable.
Probability Proportional to Size (PPS) Sampling
• A sample is said to be chosen with probabilityproportional to size if the probability of selectionfor each unit in the population is proportional tosome measure of the size of the unit.
Determining Probability ofSelection for MPPS Design
• Probability = Max (PPS1, PPS2, ...,PPSK)(for 1 to k commodities)
• Sample Weight = 1 / Probability
Determining Probabilities ofSelection for MPPS
• Probability =
Total for State 1( Farm control 1
Max ,..., Farm control K
Total for State K)n1 * nK *
(for 1 to K commodities)
1. Select a GENERAL sample with n=5 for cropland and n=5 for capacity
Record Control Control Relative Relative Probabilit
yProbabilit
y Max Prob Random In ExpNumber Data Data Measure Measure of of of Number Sample Factor
Cropland Capacity Col 2 / Col 3 / Selection Selection Selection = 1 1 / col 8(000) 10000 10000 Col 4 *n Col 5 *n Max(6,7)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)1 2000 1200 0.200 0.120 1.000 0.600 1.000 0.1603 1 1.0002 1800 800 0.180 0.080 0.900 0.400 0.900 0.98563 1500 700 0.150 0.070 0.750 0.350 0.750 0.2247 1 1.3334 1400 600 0.140 0.060 0.700 0.300 0.700 0.4889 1 1.4295 800 700 0.080 0.070 0.400 0.350 0.400 0.0972 1 2.5006 600 300 0.060 0.030 0.300 0.150 0.300 0.86417 500 0.050 0.000 0.250 0.000 0.250 0.72998 400 500 0.040 0.050 0.200 0.250 0.250 0.98749 300 0.030 0.000 0.150 0.000 0.150 0.1318 1 6.667
10 250 150 0.025 0.015 0.125 0.075 0.125 0.153011 200 100 0.020 0.010 0.100 0.050 0.100 0.295212 100 0.010 0.000 0.050 0.000 0.050 0.382913 60 100 0.006 0.010 0.030 0.050 0.050 0.228314 50 50 0.005 0.005 0.025 0.025 0.025 0.438215 30 0.003 0.000 0.015 0.000 0.015 0.657916 10 0.001 0.000 0.005 0.000 0.005 0.282517 1800 0.000 0.180 0.000 0.900 0.900 0.2366 1 1.11118 1500 0.000 0.150 0.000 0.750 0.750 0.845919 1000 0.000 0.100 0.000 0.500 0.500 0.0659 1 2.00020 500 0.000 0.050 0.000 0.250 0.250 0.9685
Total 10000 10000 1 1 5 5 7.47 7 16.040
Sampling Exercise: Multivariate Probability Proportional to Size (MPPS)
Multivariate Probability Proportional To Size Sampling (MPPS)
πi min 1, max n1
x3/41,i
Ni 1
x3/41,i
, ... ,nK
x 3/4k,i
Ni 1
x3/4k,i
(1)
Yk Nj 1
xk,j
ni 1
wi Yk,i
ni 1
wixk,i
(2)
V(Yk)
Nj 1
xk,j
2
ni 1
wix
k,i
2 n
i 1w 2
i e2k,i where e
k,i Yk,i x
k,i
nl 1
wl Yk,l
nl 1
wl xk,l
and wi
1πi
(3)
3) To integrate the statistical needs for differentlevels of government
* National * Provincial * Prefecture * County
Separate samples are now used for each administrative level
Samples are not additive
Sample Sizes – MPPS Design
Separate samples were selected in order to accommodate different levels of government
• Part A --- Funded by Provincial Government
• Part B --- Funded by Prefecture Governments
• Part C --- Funded by County Governments
Sample Sizes
• Part A --- 1000 Villages
• Part B --- 2000 Villages
• Part C --- 3000 Villages
Sample Options
(1) Part A ---- 1000 Villages
(2) Parts A and B ---- (1000 + 2000) 3000 Villages
(3) Parts A, B and C --- (1000 + 2000 + 3000) 6000 Villages
Sample SizesSample of Villages – Three Levels Of Government
High Priority Items
Items Province Prefecture County
Grain Area 450 40 20
Vegetables 500 50 30
Hogs
Poultry
450
500
40
100
20
40
Sample SizesSample of Villages – Three Levels Of Government
Medium Priority Items
Items Province Prefecture County
Tuber Crops
250 20 8
Orchards 350 70 30
Cattle 250 25 8
Sample SizesSample of Villages – Three Levels Of Government
Specialty Items
Items Province Prefecture County
Pond Area 200 15 5
Peanuts 150 5 5
Sample Selection Procedure
First Stage:
• Selection of villages (Using MPPS)
Second Stage:
• Selection of Households (random stratified)
* “Large” Households
* Other Households
Guangdong Province Pilot Surveys
• First pilot survey conducted in 2000 --- villages selected using MPPS in select counties
• Test survey of villages conducted in three prefectures in 2001, using MPPS for village selection
• Survey of villages (MPPS sample selection) conducted in entire province in 2002.
• Beginning in 2002, Households were sampled in selected villages.
Guangdong Province Survey - 2003
Commodity C.V. (%)
Grain Area
Vegetable Area
Tuber Crop Area
Orchard Area
Peanut Area
3.58
4.89
6.53
7.38
6.86
Hog Inventory
Poultry Inventory
5.62
6.19
Net Income
Per Capita 4.67
Future Of Agricultural Statistics In China
Expansion of MPPS Procedures - Nationwide:
• Crop Area Planted Survey.
• Livestock Survey
Agricultural Census:
• 2006