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Practical Considerations in Selecting Statistical Disclosure Methodology for Tabular Data

N ational A gricultural S tatistics S ervice Washington, D.C. Practical Considerations in Selecting Statistical Disclosure Methodology for Tabular Data. BTS Confidentiality Seminar Series, March 2003. N ational A gricultural S tatistics S ervice Washington, D.C.

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Practical Considerations in Selecting Statistical Disclosure Methodology for Tabular Data

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  1. NationalAgriculturalStatisticsService Washington, D.C. Practical Considerations in Selecting Statistical Disclosure Methodology for Tabular Data BTS Confidentiality Seminar Series, March 2003

  2. NationalAgriculturalStatisticsService Washington, D.C. Examples in the Presentation are Based on Actual Occurrences

  3. NationalAgriculturalStatisticsService Washington, D.C. Data have been changed to protect the innocent

  4. NationalAgriculturalStatisticsService Washington, D.C. Goals: • Discuss Decision Factors • Discuss Alternatives • Present Illustrations • Provide a Perspective for Future Decisions

  5. What is your data structure? Household, establishment, opinion, census data, sample results, etc… NationalAgriculturalStatisticsService Washington, D.C. DECISION FACTORS - 1

  6. NationalAgriculturalStatisticsService Washington, D.C. DECISION FACTORS - 2 What are your population characteristics? Limited variation, extremely clustered, highly skewed, etc…

  7. NationalAgriculturalStatisticsService Washington, D.C. DECISION FACTORS - 3 • Who are your customers? • Casual readers • In-depth analysts • People (companies) from the data population • Etc…

  8. NationalAgriculturalStatisticsService Washington, D.C. DECISION FACTORS - 4 • What decisions will be made by your customers? • Social Research Studies • Economic Investment Decisions • Implementation of Government Programs • Etc…

  9. NationalAgriculturalStatisticsService Washington, D.C. BASIC SUPPRESSION APPROACHES • (n, p) Rules • (p, k) Rules • (n, p, t) Rules

  10. NationalAgriculturalStatisticsService Washington, D.C. Should You Publish Your Suppression Rule? • Conventional wisdom says NO! • It might be essential for certain situations

  11. NationalAgriculturalStatisticsService Washington, D.C. BASIC NASS APPROACHES • (p, k) Rule for Ag Census • (n, p) Rule for Periodic Surveys • Special Techniques

  12. NationalAgriculturalStatisticsService Washington, D.C. SPECIAL TECHNIQUES • Signed Release Agreements (Waivers) • Geographic Combinations • Size Group Combinations • Reclassification of Categories

  13. NationalAgriculturalStatisticsService Washington, D.C. WAIVERS • Large Operations • Permission to Publish is Requested • Must Agree in Writing • Updated Annually

  14. Waiver Example 1/ Assumes One person controls all Arizona Production 2/ Includes AZ, AR, CA, FL, KS, MS, NC, OK, SC

  15. Waiver Example

  16. NationalAgriculturalStatisticsService Washington, D.C. Geographic Combinations

  17. NationalAgriculturalStatisticsService Washington, D.C. Geographic Combinations

  18. Size Group Example

  19. Size Group Example

  20. Reclassification Example However, assume that deWolf is a new variety planted only on one large farms

  21. Reclassification Example

  22. Agricultural Marketing Service implementation of mandatory price reporting law illustrates basic decision factor principles. NationalAgriculturalStatisticsService Washington, D.C. CASE STUDY

  23. NationalAgriculturalStatisticsService Washington, D.C. OUTLINE • Define the problem • Explain the approach • Describe the solution • Present some results

  24. NationalAgriculturalStatisticsService Washington, D.C. Large meat packers must report details of all purchase transactions.

  25. NationalAgriculturalStatisticsService Washington, D.C. Data must be reported by fixed times each day.ANDSummaries published an hour later.

  26. NationalAgriculturalStatisticsService Washington, D.C. AMS must protect confidentiality in issuing summaries.

  27. NationalAgriculturalStatisticsService Washington, D.C. 90% of slaughteris in 114 plants, owned by 65 companies.

  28. NationalAgriculturalStatisticsService Washington, D.C. 4 Companies: • 80% of fed cattle • 80% of fed lambs • 55% of all hogs

  29. NationalAgriculturalStatisticsService Washington, D.C. AMS adopted a 3/60 standard for each data cell.

  30. NationalAgriculturalStatisticsService Washington, D.C. At least three companies and no company exceeding 60%.

  31. NationalAgriculturalStatisticsService Washington, D.C. AMS never identified how many companies were in an aggregate.

  32. NationalAgriculturalStatisticsService Washington, D.C. AMS did not distinguish blank cells from suppressed cells.

  33. NationalAgriculturalStatisticsService Washington, D.C. Many (24 %) daily reports were suppressed plus many cells in released reports.

  34. NationalAgriculturalStatisticsService Washington, D.C. Some observers calculated 90% suppression.

  35. NationalAgriculturalStatisticsService Washington, D.C. When in Doubt – Examine the Data!

  36. NationalAgriculturalStatisticsService Washington, D.C. SEQUENCE DAY

  37. NationalAgriculturalStatisticsService Washington, D.C. When are proprietary datanot unique?

  38. NationalAgriculturalStatisticsService Washington, D.C. A new 3/70/20 confidentiality standard based on 60-days of data.

  39. NationalAgriculturalStatisticsService Washington, D.C. At least 3 companies operated 50% of the time.

  40. NationalAgriculturalStatisticsService Washington, D.C. No company had more than 70 percent of the volume.

  41. NationalAgriculturalStatisticsService Washington, D.C. No company would be exposed more than 20% of the time.

  42. NationalAgriculturalStatisticsService Washington, D.C. Nearly all cattle daily reports and all cells now released.

  43. NationalAgriculturalStatisticsService Washington, D.C. EXAMPLE TALLY Cattle Open Market, One Region, Daily

  44. NationalAgriculturalStatisticsService Washington, D.C. EXAMPLE TALLYCattle Forward Contracts, National, Daily

  45. NationalAgriculturalStatisticsService Washington, D.C. Modification 1 Cattle forward contracts are now published weekly

  46. NationalAgriculturalStatisticsService Washington, D.C. Modification 2 All swine packer sales alternatives weighted together daily.

  47. NationalAgriculturalStatisticsService Washington, D.C. Modification 3 Lamb purchases accumulated until the 3/70/20 is reached.

  48. NationalAgriculturalStatisticsService Washington, D.C. Author Contact Information • Rich Allen • Deputy Administrator, NASS • Room 5905 South Building • 1400 Independence Ave., S.W. • Washington, D.C. 20250-2001 • 202-690-8141 Fax 202-690-1311 • rich_allen@nass.usda.gov

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