Development of a 15-item odour discrimination test (Düsseldorf Odour Discrimination Test).

A key function of the olfactory system is the detection of differences in odour quality. Therefore, a test was developed to assess odour discrimination ability in normosmic humans. Out of six monomolecular substances (capric acid, coumarin, eugenol, geraniol, phenylethyl alcohol, and vanillin) quaternary mixtures were prepared. Within one item, three odour mixtures were presented (triangle forced-choice procedure). The deviant odour contained the same substances as the two remaining odours; however, the proportions were changed. Study 1 (120 participants) aimed to select items that contribute to a high internal consistency. Study 2 (104 participants) assessed test-retest reliability, parallel test reliability and test validity. Out of 45 items, a 15-item test (Düsseldorf Odour Discrimination Test, DODT) with an internal consistency of 0.61 and medium item difficulties was prepared. The test-retest reliability of the DODT was 0.66 (test interval = 4 weeks) and the parallel test reliability 0.42. The DODT correlated significantly with the University of Pennsylvania Smell Identification Test and to a lesser extent with the phenylethyl alcohol odour threshold test. As the DODT did not correlate with the odour discrimination test of the Sniffin' Sticks, the two tests seem to measure different performances of the olfactory system.