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In statistical terms the covariance is equal to: cov(x,y) = E(xy) – E(x)* E(y) Where E stands for the expectation, which can be calculated as the summation divided by the number of observations The relation between two traits is in animal breeding mostly described as the correlation between the traits x and y. In statistical terms the estimated correlation is: r(x,y) = cov (x,y) / (st dev x * st dev y) The correlation is usually denoted as r and has a value between -1 and + 1. A plus means that two traits are positively correlated: high values of trait x coincidence in most cases with high value of y (in case r=+1 always). A negative sign means that high values of x coincidence with low values of y. |
The scheme at right illustrates scheme below illustrates in plots relationships (correlations) between two traits in three different cases:
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