Hazel's selection index ($I = b_1 P_1 + b_2 P_2 + ... + b_n P_n$) requires phenotypic and genetic variances, phenotypic and genetic covariances, and relative economic weights ($a_i$) to calculate the weighting coefficients ($b$). The individual breeding values ($A$) are what the index estimates; they are not known beforehand and thus not necessary as input parameters.

According to Falconer's quantitative genetics, inbreeding reduces heterozygosity by a factor of $F$. The change of mean due to inbreeding (inbreeding depression) for a single locus with dominance deviation $d$ and allele frequencies $p$ and $q$ is given by: $\Delta M = -2dpqF$ (so that mean $M_F = M_0 - 2dpqF$).