EPDs are the fastest way to make genetic progress in any given trait. An important metric reported with the EPD is the BIF accuracy. The accuracy gives an estimate of the predictability of the EPD reported. EPDs with lower accuracy have less information associated with that number and may be more likely to move as additional information (phenotypes and genotypes) are submitted for that animal or its relatives. A more intuitive number to talk about is possible change (PC) or confidence interval. The PC gives a range within which the EPD will land two-thirds of the time. As more information is known about that EPD, the BIF accuracy will increase and the PC will decrease (a smaller range of potential movement in the future).
Here is how it works.
An EPD +/- one PC unit tells you a range within which the animal’s EPD will land 2 out of 3 times. You can take this further. An EPD +/- two PC units tells you a range within which the animal’s true EPD will land 95% of the time. And even further. An EPD +/- three PC units tells you a range within which the animal’s EPD will land 99% of the time.
For example, if a bull has a Calving Ease EPD of 12.0 and a PC of 3.0, the following is true.
- ⅔ of the time, the bull’s CE EPD will land between 9.0 and 15.0 (12.0 +/- 3.0). This also means ⅓ of the time the bull’s CE EPD will land either below 9.0 or above 15.0.
- 95% of the time, the bull’s CE EPD will land between 6.0 and 18.0 (12.0 +/- 6.0). 5 out of 100 bulls will land outside that range.
- 99% of the time, the bull’s CE EPD will land between 3.0 and 21.0 (12.0 +/- 9.0). 1 out of 100 bulls will land outside this range.
“Accuracy, particularly BIF accuracy, is commonly misunderstood and thus misused by beef producers and allied industry. A much more useful metric to gauge the potential of an animal’s EPD to change with additional information is possible change. Possible change values can be used to provide a degree of confidence that an animal’s true EPD is within a given range and thus enable a producer to consider the risk associated with purchasing a bull or semen whose true EPD might fall outside of a desired range.” - Matt Spangler, Ph.D., Professor University of Nebraska - Lincoln
The ASA Board of Trustees recently passed a directive to add PC to the main animal page on Herdbook. In August, PC will be added to the main animal page directly beneath the EPD/Index row. For the time being, BIF accuracy will still be published on the main animal page.