Abstract: An analyser and method for determining the relative importance of fractions of biological mixtures projects data obtained from at least two mixtures with different physiological conditions by chromatographic or mass spectrometric measurement into a second attribute space using a projection technique such as principal component analysis. The projected data is then filtered using a feature selection method such as ReliefF, before being projected back to the first attribute space using a reversion of the projection technique. This back-projected data is then filtered using another feature selection method such as ReliefF before being output in a human-readable form.