The Master Curve methodology is now widely used for ensuring the integrity of ferritic steel structures against brittle fracture. The methodology has been recently extended to the treatment of macroscopically inhomogeneous materials through bimodal and multimodal approaches. This can be of practical importance in many applications. However, the conditions of applicability of those advanced techniques remain a weak point. In this work, it is shown that a probabilistic approach can provide guidance to select the appropriate method and to measure the confidence level in statements about inhomogeneity. The method proposed is applied successfully to a practical case.