A robust, brief measure of an individual's most preferred level of salt in an ordinary foodstuff

A single-session procedure to assess an individual's most preferred level of a factor in a product is justified theoretically and illustrated by the results for salt concentration in samples of bread and tomato soup tested on 30 young men who had had no previous experience of the task. Each man rated the saltiness of each sample as a distance below or above his ideal for that food type. Without the rater knowing, his stimulus set was coordinated to his rating responses in order to minimise biases in what others have shown can be a linear response mode. The Weber fraction is constant for the medium range of NaCl solutions when concentration units are used, and so Fechner's principle of direct scaling was applied: mean linear regressions between ideal-relative intensity responses and the logarithm of salt concentrations in each individual were nearly always statistically reliable with only six to 20 ratings of three to six salt levels in bread or soup. Values of the regression intercepts for bread at the initial session and five months later correlated significantly, as also did the regression slopes. Thus, a robust value for each individual's ideal salt level for each food could be interpolated from the regression equation. There was no effect of sequence of bread and soup sessions. Bread and soup salt-ideals were correlated, as were their slopes. A regression slope appears to represent an individual's tolerance of deviations from ideal. The relation of the slope to choice behaviour, and its relative dependence on intensity sensitivity and a preference motivation characteristic of the individual and test situation, remain to be elucidated. This procedure should have wide application in consumer preference measurement.