Bühlmann–Straub credibility factor
= Bühlmann–Straub credibility factor
{c}
{title2=$Z=\frac{Wa}{Wa+v}$}
The experience weight is $Z=Wa/(Wa+v)$, where $W$ is total observed exposure, $a$ the <variance of hypothetical means>, and $v$ the <expected process variance>. With positive $a$, it is $W/(W+v/a)$. More exposure raises the weight; larger process noise lowers it. If $a=0$, the unknown conditional mean is constant and one can set $Z=0$.