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

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

Webster 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

Static? Yearling EPD of +100 for YW ◦+100 after 50 progeny?

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

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

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

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

True Accuracy Correlation between predicted and “true” breeding values

Relationship to BIF

Accuracy Compared

Genetic Variation Explained 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…

MBV BIF Accuracy Genetic CorrelationBIF Accuracy

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

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

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

Relative Ranking Of Measures True Accuracy Not used in U.S. Beef Industry % GV Used in context of Genomic Tests BIF Accuracy U.S. Beef Standard Used with all EPDs

Reducing Risk 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”

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

Take Home 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

Questions?