Assessing the similarity of odours by sorting and by triadic comparison

The odours of five carbonyls (heptanone, octanone, octenal, nonenal and decadienal) and the pair-wise mixtures of each ketone with each aldehyde were compared using two non-scaler, non-descriptive procedure: sorting, and the method of triads. In the sorting procedure, 24 assessors each sorted the 11 substances into sets having similar odours. The number of times a pair of substances was put into the same set was used to construct a similarity matrix which was subjected to non-metric, multidimensional scaling by the MINISSA program to reveal similarities in odour. In the triadic presentation procedure, all the 165 possible triads of the 11 substances were presented in sets of five or six to 30 assessors who had to select the most similar and the most dissimilar pair in each triad. The data were submitted to non-metric, multidimensional scaling by the TRISOSCAL program. The two procedures were each performed on two occasions, and all four sets of data gave similar groupings of odours in the resulting plots. The ketones and aldehydes clustered at oppsite poles of the diagrams with the mixtures lying between the positions of their components.