The Many Measures of The Many Measures of Accuracy: How Are They Accuracy: How Are They

Related?Related?Matt Spangler, Ph.D.

University of Nebraska-Lincoln

Why Worry About Accuracy?Why Worry About Accuracy?

“Prediction is hard, especially about the future”

WebsterWebster

Freedom from mistake or errorConformity to truth or to a standard or

modelDegree of conformity of a measure to a

standard or true value

Static?Static?

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

Values are standard deviationsLow accuracy means larger possible

change valuesNot static

◦Different for each breed, trait, and could differ between evaluations

Possible ChangePossible Change

Possible Change TablePossible Change Table

How to Use Possible ChangeHow to Use Possible Change

Weaning Wt. EPD = 40ACC. = 0.60

Possible change +/- 4.60

68% confident his true EPD is between 35.4 and 44.6

25 30 35 40 45 50 550

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

68%

95%

Confidence Intervals for EPD = 40, Acc = 0.60, SEP = 4.6

Mating—Passing of AllelesMating—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 SamplingMendelian 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 unfavorablyMore information earlier allows you to

choose animals more accurately

Calving EaseCalving 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-CEDExample-CED

BIF AccuracyBIF Accuracy

More conservative◦More progeny to get higher values

The U.S. standardRange from 0-1

True AccuracyTrue Accuracy

Correlation between predicted and “true” breeding values

r nh2

4(n 1)h2

Relationship to BIFRelationship to BIF

r 1 (1 BIF)2

Accuracy ComparedAccuracy Compared

Genetic Variation ExplainedGenetic 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 AccuracyMBV BIF Accuracy

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

TestTest

BW EPD -1.0 with accuracy (BIF) of .9050K Prediction for BW explaining 50% GV

What To Use?--GeneticsWhat To Use?--Genetics

Any of the measures described can be used

But not directly comparedEasiest if they were on the same scale

What To Use--ManagementWhat To Use--Management

Different ball of waxInterested in proportion of phenotypic

variation explainedNo metrics available to do this

Relative Ranking Of MeasuresRelative Ranking Of Measures

Reducing RiskReducing Risk

Accuracy is importantNot much difference between yearling

bullsMA-EPD could create differencesBull buyers will have to look at accuracyAccuracy helps determine the “benefit”

It Doesn’t Work…It Doesn’t Work…

“I’ve used high accuracy calving ease bulls and had big calves”

Environment?Cow?Within sire variation?

Take HomeTake Home

Pay attention to accuracyThere are different measures

◦They are not “apples to apples”Right now you have to do the mathYou need to know how to equate BIF

accuracy to %GVIf a sire has a high accuracy then

additional information does very little

Questions?Questions?