Variance of hypothetical means
= Variance of hypothetical means
{title2=$a=\operatorname{Var}(\mathbb E[X\mid\Theta])$}
The variance of hypothetical means in the <Bühlmann model> is the between-risk <variance> of the conditional claim <expected value>. It creates the shared <covariance> $a$ between different years of the same risk and determines how much individual experience should influence the premium.