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The better we can express the phenotypic superiority and the higher the repeatability, the better we should be able to estimate the breeding value. Indeed this is the case. Repeated records allow for a better estimate of the regression coefficient. In case of a single record the regression coefficient is h2, but if there are multiple records it becomes:
| Paneel | ||
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bmass selection, multiple records = nh2 / 1+ r (n-1) |
where n is the number of repeated records, and r is the correlation between subsequent records: the repeatability. If the repeatability is 0.5 and we have 2 records, than the regression coefficient increases from h2 to 2h2 / 1.5 = 1.33 h2. The value of repeated observations depend on the repeatability and on the number of records that are available. The lower the repeatability, the more repeated observations are influenced by different environmental influences, and the more added value it has to collect multiple records and re-estimate the breeding value every time a new own performance record becomes available.
Thus:
| Paneel | ||
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Repeatability is the correlation between subsequent records: the more they are alike, the higher the repeatability (max =1) Repeated observations on own performance adds to the estimation of the regression coefficient. The lower the repeatability, the higher the added value of repeated observations. |