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The Many Measures of Accuracy: How Are They Related?

The Many Measures of Accuracy: How Are They Related?. Matt Spangler, Ph.D. University of Nebraska-Lincoln. “Prediction is hard, especially about the future”. Why Worry About Accuracy?. Freedom from mistake or error Conformity to truth or to a standard or model

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The Many Measures of Accuracy: How Are They Related?

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  1. The Many Measures of Accuracy: How Are They Related? Matt Spangler, Ph.D. University of Nebraska-Lincoln

  2. “Prediction is hard, especially about the future” Why Worry About Accuracy?

  3. Freedom from mistake or error • Conformity to truth or to a standard or model • Degree of conformity of a measure to a standard or true value Webster

  4. Yearling EPD of +100 for YW • +100 after 50 progeny? Static?

  5. Values are standard deviations • Low accuracy means larger possible change values • Not static • Different for each breed, trait, and could differ between evaluations Possible Change

  6. Possible Change Table

  7. Weaning Wt. EPD = 40 ACC. = 0.60 Possible change +/- 4.60 68% confident his true EPD is between 35.4 and 44.6 How to Use Possible Change

  8. 68% 95% Confidence Intervals for EPD = 40, Acc = 0.60, SEP = 4.6

  9. Mating—Passing of Alleles

  10. Why the low correlations (accuracy) for yearling bulls? • Uncertainty surrounding what alleles were received from parents • We begin to understand this when an animal has a record • Becomes more clear as we see what it is passing on to its offspring • Commercial producers do not have this luxury Mendelian Sampling

  11. Two yearling bulls with a +5 CED EPD with accuracy of 0.2. • Possible change of 6 • With the addition of more information their EPDs change • One favorably and the other unfavorably • More information earlier allows you to choose animals more accurately Calving Ease

  12. Bull A Bull B • +5 +5 • Addition of progeny information • Bull A Bull B • -1 +11 • In this extreme case risk was 12% more calving difficulties • Average is still +5* Example-CED

  13. More conservative • More progeny to get higher values • The U.S. standard • Range from 0-1 BIF Accuracy

  14. Correlation between predicted and “true” breeding values True Accuracy

  15. Relationship to BIF

  16. Accuracy Compared

  17. The proportion of variation due to additive genetics of a single trait explained (by a genomic test) • Range between 0 and 100% • A test explains 49% of the GV for a trait… Genetic Variation Explained

  18. MBV BIF Accuracy

  19. BW EPD -1.0 with accuracy (BIF) of .90 50K Prediction for BW explaining 50% GV Test

  20. Any of the measures described can be used • But not directly compared • Easiest if they were on the same scale What To Use?--Genetics

  21. Different ball of wax • Interested in proportion of phenotypic variation explained • No metrics available to do this What To Use--Management

  22. Relative Ranking Of Measures

  23. Accuracy is important • Not much difference between yearling bulls • MA-EPD could create differences • Bull buyers will have to look at accuracy • Accuracy helps determine the “benefit” Reducing Risk

  24. “I’ve used high accuracy calving ease bulls and had big calves” • Environment? • Cow? • Within sire variation? It Doesn’t Work…

  25. Pay attention to accuracy • There are different measures • They are not “apples to apples” • Right now you have to do the math • You need to know how to equate BIF accuracy to %GV • If a sire has a high accuracy then additional information does very little Take Home

  26. Questions?

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