Geometrical interpretation of the linear mixture model. Concentration vectors of the linear mixture model comprised of control reference sample and test sample, (2a) and Figure 1a, i.e. disease reference sample and test sample, (2b) and Figure 1b, are confined in a first quadrant of the plane spanned by two mixture samples. Features (m/z ratios or genes) with prevailing concentration in disease sample are linearly combined into component associated with the red colour relative concentration vector. Likewise, features with prevailing concentration in control sample are combined linearly into component associated with the blue colour relative concentration vector. Features that are not differentially expressed are combined linearly into one or more neutral components associated with the green colour relative concentration vectors.