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Corn Export Cargo Quality Report 2013/2014

Contents

  1. Export Cargo Quality Highlights
  2. Introduction
  3. Quality Test Results
  4. Moisture
  5. Chemical Composition
  6. Physical Factors
  7. Mycotoxins
  8. U.S. Corn Export System
  9. U.S. Export Corn Flow
  10. Impact of the Corn Market Channel on Quality
  11. U.S. Government Inspection and Grading
  12. Survey and Statistical Analysis Methods
  13. Survey Design and Sampling
  14. Statistical Analysis
  15. Testing Analysis Methods
  16. Corn Grading Factors
  17. Moisture
  18. Chemical Composition
  19. Physical Factors
  20. Mycotoxin Testing
  21. U.S. Corn Grades and Conversions
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C. Statistical Analysis

The sample test results for the grade factors, moisture, chemical composition and physical factors were summarized as the U.S. Aggregate and also by the three ECAs (Gulf, Pacific Northwest and Southern Rail) and two “contract grade” categories. Contract grades are described in the “Corn Export System” section on page 39. The two contract grade categories in the Export Cargo Report are:

  • “U.S. No. 2” or “U.S. No. 2 or better” contracts specify that the corn must at least meet U.S. No. 2 factor limits or be better than U.S. No. 2 factor limits. This category is designated as U.S. No. 2 o/b.
  • “U.S. No. 3” or “U.S. No. 3 or better” contracts specify that the corn must at least meet U.S. No. 3 factor limits or be better than U.S. No. 3 factor limits. This category is designated as U.S. No. 3 o/b.

The sampling process resulted in a surplus sample in the Gulf ECA (which provided a slightly greater sampling density in that ECA) and less than the targeted number of samples in the Southern Rail ECA. However, the U.S. Aggregate averages and standard deviations were weighted by ECA using the original sampling proportions. The Relative ME was calculated for each of the quality factors tested for this study at the U.S. Aggregate level and for each of the ECAs.

The Relative ME was less than ± 10% for all the quality attributes at the U.S. Aggregate level and for the Gulf ECA. The Relative ME exceeded ± 10% for some quality factors (see table below) in the Pacific Northwest and Southern Rail ECAs.

While the lower level of precision for these quality factors in the two ECAs is less than desired, the levels of Relative ME do not invalidate the estimates. The averages for the quality factors are the best possible unbiased estimates of the true population means. However, they are estimated with greater uncertainty than the quality factors with a Relative ME less than ± 10%. Footnotes in the summary tables for “Grade Factors and Moisture” and “Physical Factors” indicate the attributes for which the Relative ME exceeds ± 10%. This allows the reader to keep in mind the greater degree of uncertainty of the sample average representing the true population mean.

References in the “Quality Test Results” section to statistical differences were validated by 2-tailed t-tests at the 95% confdence level. The t-tests were calculated:

  • Between factors in the Harvest Report 2013/14 and Export Cargo Report 2013/14,
  • Between factors in the Export Cargo Report 2013/14 and Export Cargo Report 2012/13, and the Export Cargo Report 2013/14 and Export Cargo Report 2011/12,
  • Among factors in the Export Cargo Report 2013/14 ECAs (Gulf, Pacific Northwest, Southern Rail), and
  • Between chemical and physical factors in the Export Cargo Report 2013/14 contract grades (U.S. No. 2 o/b, U.S. No. 3 o/b).