.. _DefBLVarianceLearning:

Definition of Term: Bayes linear variance learning
==================================================

Learning about the variance :math:`\sigma^2` of a complex model can be a
challenging problem. The Bayes Linear approach is to make a standard
Bayes Linear :ref:`adjustment<DefBLAdjust>` of our prior beliefs
about :math:`\sigma^2` using the observed sample variance and exploiting
certain weak assumptions about model behaviour (:ref:`second-order
exchangeability<DefSecondOrderExch>`).