A key part of this problem is that an inspector only has access to data from a small inspected area. In this area, there is only one minimum thickness, which does not provide enough information to build a model of the smallest thicknesses. An inspector can generate a sample of the smallest thickness measurements by partitioning the inspection data into a number of equally sized blocks. In each block the minimum thickness is recorded. This set forms a sample of the smallest thickness measurements. From this sample, one can build a model which takes into account the variations of the smallest thickness measurements. Extreme value analysis (EVA) provides a limiting form for this model. It states that, if the underlying thickness measurements in each block are taken from independent and identical distributions, then the sample of minimum thickness measurements will follow a generalized extreme value distribution (GEVD).
