Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, that obtain a first machine learning model that is configured to output a score. The training examples can each include feature values that represent features of an item, and an outcome label for the item. From the training examples, training pairs of training examples are determined. For each training pair: (i) a score is generated for each training example in the training pair using the first machine learning model; and (ii) for the training pair, a score difference of the scores generated for the training examples in the training pair is determined. Using the training pairs and the score differences, a second machine learning model is trained to produce score differences that, for the same training examples, are within a threshold value of the score differences produced by the first machine learning model.

Abstract: Provided is an odour sensor which may be useful for discriminating between the odour of human or other mammalian individuals, and perimidine monomers and polymers which may be used in such a sensor.