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 Degree of conformity of a measure to a standard or true value Webster Yearling EPD of +100 for YW ◦ +100 after 50 progeny? Static? 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 Possible Change Table 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 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 25 30 35 40 45 50 55 68% 95% Confidence Intervals for EPD = 40, Acc = 0.60, SEP = 4.6 Sire Dam Mating—Passing of Alleles 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 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 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 More conservative ◦ More progeny to get higher values The U.S. standard Range from 0-1 BIF Accuracy Correlation between predicted and “true” breeding values 2 nh r 2 4 (n 1)h True Accuracy r 1 (1 BIF) Relationship to BIF 2 Accuracy Compared 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 Genetic Correlation BIF Accuracy 0.1 0.005 0.2 0.020 0.3 0.046 0.4 0.083 0.5 0.132 0.6 0.2 0.7 0.286 MBV BIF Accuracy BW EPD -1.0 with accuracy (BIF) of .90 50K Prediction for BW explaining 50% GV Test Any of the measures described can be used But not directly compared Easiest if they were on the same scale What To Use?--Genetics Different ball of wax Interested in proportion of phenotypic variation explained No metrics available to do this What To Use--Management True Accuracy % GV BIF Accuracy • Not used in U.S. Beef Industry • Used in context of Genomic Tests • U.S. Beef Standard • Used with all EPDs Relative Ranking Of Measures 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 “I’ve used high accuracy calving ease bulls and had big calves” Environment? Cow? Within sire variation? It Doesn’t Work… 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 Questions?