A simple and reliable method for clinical assessment of odor thresholds.

We investigated whether presenting of dilutions of phenyl ethyl alcohol at random succession according to the method of constant stimuli can replace the standard procedure of presenting a various number of dilutions in a staircase paradigm. Forty-six men and 44 women, aged 19-76 years, participated in this study. Phenyl ethyl alcohol was diluted in a ratio of 1:2, starting from 4%. Presentation of the odorant followed a three-alternative, temporal forced-choice paradigm with two blanks in addition to the odorant. Twenty dilutions were administered in a randomized order. Odor threshold was obtained by logistic regression of the correct and incorrect identifications of the probe containing the odorant. Thresholds were also calculated on the basis of the first 16 dilution steps only. Results from these procedures were compared with 'gold-standard' threshold assessment employing a three-alternative, temporal forced-choice staircase paradigm with seven reversals using 16 dilutions of phenyl ethyl alcohol. The method of constant stimuli took a shorter and less variable testing time than the staircase technique. The use of 20 dilution steps provided no better results than the use of 16 steps. The method of constant stimuli exhibited a good test-retest reliability (r = 0.7; P < 0.001) comparable to that of the staircase method and provided unbiased results highly correlated (r = 0.8; P < 0.001) with those of the staircase technique with similar inter-test variability. Applying 16 dilutions (1:2 steps) of phenyl ethyl alcohol at random succession in a three-alternative, temporal forced-choice paradigm is thus a simple and reliable procedure for the reproducible assessment of odor thresholds that may be contemplated as an alternative to the 'gold-standard' staircase method of clinical odor threshold assessment.