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Building & Using Area Sampling Frames for Agricultural Censuses & Surveys

Building & Using Area Sampling Frames for Agricultural Censuses & Surveys. presented by Theresa “Terry” Holland National Agricultural Statistics Service U.S. Department of Agriculture Regional Workshop on Sampling for Agricultural Surveys 21 June 2011 Montevideo, Uruguay. Definitions.

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Building & Using Area Sampling Frames for Agricultural Censuses & Surveys

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  1. Building & Using Area Sampling Frames for Agricultural Censuses & Surveys presented by Theresa “Terry” Holland National Agricultural Statistics Service U.S. Department of Agriculture Regional Workshop on Sampling for Agricultural Surveys 21 June 2011 Montevideo, Uruguay

  2. Definitions sampling frame: • a means by which a target populationmay be sampled • a list of all sampling units &a set of rules for identifyingpopulation units

  3. Definitions target population all the items (people, farms, animals, businesses, etc.)about which information is needed sampling units well-defined units that allow access to the target population population units individual elements of the target population

  4. Sampling Frames List frames: farmers agri-businesses fields or orchards Area frame: segments of land

  5. NASS List Frame What is it? data to identify, locate & contactfarmers & agri-businesses name address telephone number state, district & county Social Security Number Employer Identification Number data about the farm/business total acres individual crop acres grain storage capacity peak livestock inventories peak number of hired workers . . .

  6. NASS List Frame How is it constructed? sources for new names & data growers organizations farm program lists state & local tax records state & local license records lists from other federal, state & local agencies newspaper & magazine articles sources for updating names & data on-going NASS surveys Census of Agriculture

  7. NASS List Frame How is it used?

  8. NASS List Frame 1997

  9. NASS List Frame 2005

  10. NASS List Frame Strengths: • can use inexpensive data collection methods (mail, telephone) • can target specific or rare commodities • can reduce variability due to sampling • cost efficient

  11. NASS List Frame Weaknesses: • does not cover entire population • goes out-of-date quickly • increased non-sampling errors due todata collection methods • requires on-going maintenance build update remove duplication remove out-of-scope records

  12. NASS List Frame Coverage:

  13. NASS List Frame Sampling Techniques: • Simple Random Sampling (SRS) • Systematic Sampling • Stratified Sampling • Probability Proportional to Size (PPS) • Multivariate Probability Proportional to Size (MPPS) • Permanent Random Number (PRN)

  14. NASS Area Frame What is it? land area of the U.Sdivided into segmentsusing physical boundaries associate farms, crops, animals, etc.with land inside the segments

  15. NASS Area Frame How is it constructed? using… satellite imagery digital maps GIS software aerial photography • divide land area into strata based on land use& likelihood of finding agriculture • subdivide land use strata into strata blocks • select a sample of strata blocks • subdivide selected strata blocks into segments

  16. NASS Area Frame

  17. NASS Area Frame Satellite imagery:

  18. NASS Area Frame Digital map features:

  19. NASS Area Frame Strata blocks - primary sampling units (PSUs):

  20. NASS Area Frame Land use stratification for Illinois:

  21. NASS Area Frame Selected PSU & segment:

  22. NASS Area Frame Land Use Strata & Sampled Segments:

  23. NASS Area Frame How is it used?

  24. NASS Area Frame 2007

  25. NASS Area Frame Data Collection Tools: Road map Aerial photo

  26. NASS Area Frame Data collection:

  27. NASS Area Frame “Segment” sample estimators: h = land use stratum j = stratum block within stratum h k = segment within stratum block j m = farming operation within segment k ehjk = expansion factor for selected segment k whjkm = weight for farming operation m xhjkm = survey value for farming operation m Nh = number of possible segments in stratum h nh = number of segments sampled in stratum h

  28. NASS Area Frame “Segment” sample estimators: Closed whjkm = 1 xhjkm = value of item within segment only Open whjkm = 1 if farmer resides in segment, 0 otherwise xhjkm = value of item for entire farming operation Weighted whjkm = percent of total farm area within the segment xhjkm = value of item for entire farming operation

  29. NASS Area Frame Strengths: • complete coverage • reduced non-sampling errors • estimates well for commonly produced commodities • versatility • longevity

  30. NASS Area Frame Weaknesses: • expensive (frame construction & data collection) • difficult to target specific or rare commodities • sensitive to outliers • can be inefficient • requires definable physical boundaries

  31. NASS Multiple Frame What is it? a way to take advantage of strengthsof both list & area frames area– complete list– efficient population➚

  32. NASS Multiple Frame How is it used?

  33. Area List Windy Ridge Farm John Brown 1234 Farm Rd Anywhere, US 00000 Richard Jones 789 Ranch Rd Anystate, US 99999 Bob Smith 56 Orchard Rd Anywhere, US 00000 Dave White 123 Farm Rd Anywhere, US 00000 NASS Multiple Frame

  34. NASS Multiple Frame Strengths: • together frames cover target population • can control variability due to sampling • can control costs with large list, small area samples • can target specific or rare commodities

  35. NASS Multiple Frame Weaknesses: • NOL can be too small • overlap determination can be difficult • errors in overlap determination canbias estimates • list and area frames must bemaintained independently

  36. Other Types of Area Frames segments based on latitude & longitude sampling unit = segment of land using latitude & longitude as boundaries associate farms, land, animals, etc. with land inside the segment segments based on random points sample unit = segment constructed around random point according to specific rules associate farms, land, animals, etc. with land inside or touching the segment random points sample unit = random point associate farms, land, animals, etc. with operator of land at the point

  37. Nigeria Area Frame – Pilot in Kaduna State Satellite imagery:

  38. Nigeria Area Frame – Pilot in Kaduna State Strata blocks:

  39. Nigeria Area Frame – Pilot in Kaduna State Land Use Strata & Sampled Points:

  40. Nigeria Area Frame – Pilot in Kaduna State How is it used?

  41. Nigeria Area Frame – Pilot in Kaduna State

  42. Nigeria Area Frame – Pilot in Kaduna State Data Collection Tools: Satellite maps GPS

  43. Nigeria Area Frame – Pilot in Kaduna State Data collection:

  44. Nigeria Area Frame – Pilot in Kaduna State “Point” sample estimator: i = land use stratum j = selected point within stratum Li = total land in stratum i ni = total number of points sampled in stratum i eij = expansion factor for selected point j within stratum i pij = population indicator for point j in stratum i xij = survey value for point j in stratum i lij = total land in farm identified by point j in stratum i

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