Data were obtained from 9139 subjects [4928 females aged 5–96 years (M = 31.8, SD = 18.9) and 4211 males aged 5–91 years (M = 30.7, SD = 17.7)]. Among them, 3432 (37.5%) had been included in a previous study to establish normative data [15 (link)]. According to the inclusion criteria for the respective studies, all subjects were healthy and none reported histories for any olfactory disturbances.
Odors were delivered using felt-tip pens (“Sniffin’ Sticks”) of approximately 14 cm length and an inner diameter of 1.3 cm. These pens carry a tampon soaked with 4 ml of liquid odorant. For odor presentation, the cap was removed from the pen for approximately 3 s, the pen’s tip brought in front of the subject’s nose and carefully moved from left to right nostril and backwards [3 (link)].
The threshold was obtained in a three alternative forced choice paradigm (3 AFC) where subjects were repeatedly presented with triplets of pens and had to discriminate one pen containing an odorous solution from two blanks filled with the solvent. Phenylethanol (dissolved in propylene glycol) or n-butanol (dissolved in water) were used, with both odorants having been found equivalent in olfactory sensitivity testing: scores obtained with both are correlated [17 (link)]. The highest concentration was a 4% odor solution. Sixteen concentrations were created by stepwise diluting previous ones by 1:2. Starting with the lowest odor concentration, a staircase paradigm was used where two subsequent correct identifications of the odorous pen or one incorrect answer marked a so-called turning point, and resulted in a decrease or increase, respectively, of concentration in the next triplet. Triplets were presented at 20 s intervals. The threshold score was the mean of the last four turning points in the staircase, with the final score ranging between 1 and 16 points.
The discrimination task used the same 3 AFC logic. Two pens of any triplet contained the same odorant, while the third pen smelled differently. Subjects were asked to indicate the single pen with a different smell. Within-triplet intervals were approximately 3 s. As the odors used in this subtest were more intense, between-triplets intervals were 20–30 s. The score was the sum of correctly identified odors. Hence, the scores in this task ranged from 0 to 16 points. Importantly, subjects were blindfolded for the threshold and discrimination tasks to avoid visual identification of target pens.
Odor identification comprised common and familiar odorants (recognized by at least 75% of the population). Subjects were presented with single pens and asked to identify and label the smell, using four alternative descriptors for each pen. Between-pen intervals were approximately 20–30 s. The total score was the sum of correctly identified pens, thus subjects could score between 0 and 16 points.
The final “TDI score” was the sum of scores for Threshold, Discrimination and Identification subtests, with a range between 1 and 48 points.
Odors were delivered using felt-tip pens (“Sniffin’ Sticks”) of approximately 14 cm length and an inner diameter of 1.3 cm. These pens carry a tampon soaked with 4 ml of liquid odorant. For odor presentation, the cap was removed from the pen for approximately 3 s, the pen’s tip brought in front of the subject’s nose and carefully moved from left to right nostril and backwards [3 (link)].
The threshold was obtained in a three alternative forced choice paradigm (3 AFC) where subjects were repeatedly presented with triplets of pens and had to discriminate one pen containing an odorous solution from two blanks filled with the solvent. Phenylethanol (dissolved in propylene glycol) or n-butanol (dissolved in water) were used, with both odorants having been found equivalent in olfactory sensitivity testing: scores obtained with both are correlated [17 (link)]. The highest concentration was a 4% odor solution. Sixteen concentrations were created by stepwise diluting previous ones by 1:2. Starting with the lowest odor concentration, a staircase paradigm was used where two subsequent correct identifications of the odorous pen or one incorrect answer marked a so-called turning point, and resulted in a decrease or increase, respectively, of concentration in the next triplet. Triplets were presented at 20 s intervals. The threshold score was the mean of the last four turning points in the staircase, with the final score ranging between 1 and 16 points.
The discrimination task used the same 3 AFC logic. Two pens of any triplet contained the same odorant, while the third pen smelled differently. Subjects were asked to indicate the single pen with a different smell. Within-triplet intervals were approximately 3 s. As the odors used in this subtest were more intense, between-triplets intervals were 20–30 s. The score was the sum of correctly identified odors. Hence, the scores in this task ranged from 0 to 16 points. Importantly, subjects were blindfolded for the threshold and discrimination tasks to avoid visual identification of target pens.
Odor identification comprised common and familiar odorants (recognized by at least 75% of the population). Subjects were presented with single pens and asked to identify and label the smell, using four alternative descriptors for each pen. Between-pen intervals were approximately 20–30 s. The total score was the sum of correctly identified pens, thus subjects could score between 0 and 16 points.
The final “TDI score” was the sum of scores for Threshold, Discrimination and Identification subtests, with a range between 1 and 48 points.