The present invention relates principally to the statistical analysis of protein separation patterns. Specifically, the invention provides a method of performing operations on protein samples for the analysis of separation patterns, the method including separating a plurality of protein samples to produce a plurality of respective separation patterns; forming a representation of each separation pattern; building an importance map by iteratively recording performance values of classification models against locations in the importance map which correspond to locations in representations of separation patterns of data points used to build the classification models; and processing the importance map to identify important areas. Parts of the map which include high performance values indicate regions of the separation pattern which are statistically important in predicting a classification of the pattern.