These kinds of errors are expected and can be accounted for in sire evaluation models. Errors that result from laxity or willful misrepresentation on the part of breeders are another matter. There is some evidence suggesting that birth weight records may not be as accurate as they could be. It is unlikely that breeders take liberties with birth weight in order to manipulate sire evaluation, but widespread cheating in the measurement of this trait could have this result. For the same reason that breeders often mate expensive A.I. sires to only their best producing cows, breeders are also tempted to provide preferential treatment for the calves from those matings.
Some experts feel that preferential treatment creates a serious bias in sire evaluation results.
The concept of accuracy Accuracy has been described previously in this series as a number which represents statistically the adequacy of information used to estimate breeding values and EPDs. It is essentially a function of the amount of information available. Accuracy does not, however, completely describe the reliability of an estimate. If an estimated breeding value or EPD is biased by any of the causes listed above, and if the statistical method used to calculate the EBV or EPD does not account for the bias, then the associated accuracy value may be misleading. If, for example, a particular sire has produced many calves in many herds, but those calves have routinely received preferential treatment, the sire's EPD for weaning weight may have high statistical accuracy, but won't be accurate at all in the more general sense of the word.