Development and validation of the MultiScent-20 digital odour identification test using item response theory

Abstract

Although validated and reliable psychophysical tests of olfactory function are available, an easy-to-use and feasible test has yet to be developed. This study aimed to design a digital odour identification test, evaluate its validity, assess its reliability, establish a normative curve, and explore the impact of demographic factors. The odour identification test was presented with the Multiscent-20, a hand-held, tablet-like digital scent device that features an integrated odour digital delivery system. The identification performance on the 20 odours was assessed using item response theory (IRT). The normative curve was established by administering the test to a large sample of participants (n = 1299). The mean identification score was 17.5 (SD = 2.1). The two-parameter logistic IRT model provided the best fit, revealing variation in item discrimination and difficulty parameters. Educational attainment influenced performance, with primary education associated with lower scores. Additionally, sex was not found to be associated with performance. This study provides initial evidence supporting the validity and reliability of use of the Multiscent-20 as a digital odour identification test. The test's automation and portability enable the standardized delivery of olfactory stimuli and efficient automatic recording and scoring of responses.

Figure 1

Item Characteristic Curves. Each curve depicts the relationship between an individual’s odour identification ability (θ, theta) on the horizontal axis and the probability of providing a correct answer to the question on the vertical axis. The person parameter (θ, latent trait, or ability) is on a scale from − 4 (severely impaired odour identification ability) to + 4 (excellent odour identification ability). The P(θ) depicted on the y-axis of each curve represents the probability of providing the correct answer on the specific item.

Figure 2

Item Information Curves. Each curve represents an item in the Multiscent-20. The shape of the curve indicates how much information the item provides at different levels of latent ability. A steeper curve indicates that the item offers more information at a given level of odour identification ability, while a flatter curve indicates that the item provides less information. The person parameter (θ, latent trait, or ability) is on a scale that goes from − 4 (low odour identification ability) to + 4 (high odour identification ability). The curves show that Menthol, Bubble-gum, Strawberry, Garlic, Onion, Pizza, Mint, and Vanilla are the most informative items.

Figure 3

Multiscent-20 test information and scale characteristic curves. The left panel displays the item information curve (red line) and the standard error (dotted brown line). The right panel presents the scale characteristic curve. The test is most informative for a range of θ values between − 4 and − 1, indicating a higher precision and better discrimination in estimating the loss of odour identification ability for individuals within this ability range.

Figure 4

MultiScent-20 Odour Identification Score: distribution and descriptive statistics of central tendencies, dispersion, and percentiles of normative performance.

Figure 5

MultiScent-20 in Olfactory Function Assessment. (A) Compares MultiScent-20 scores between chronic sinusitis patients (hyposmic group) and normosmic controls, showing a significant difference. (B) Compares scores between Parkinson’s disease patients and age-matched controls, indicating a substantial olfactory deficit in Parkinson’s. (C) Scatter plot demonstrating the convergent validity of MultiScent-20 with the Sniffin’ Sticks 16-item score. Violin plots show score distributions; central red dot is the mean. Statistical details (effect sizes, p-values, CI 95%, n obs/n pairs) are provided.

Figure 6

Front (left) and back (right) views of the Multiscent-20. It is a dedicated tablet with a 7-inch touchscreen used to present aromas and record responses digitally. The opening for odour release is indicated by an arrow on the front of the device. The fragrance capsule is also shown. The device can be loaded with up to 20 capsules made of oil-resistant polymer, in which olfactory stimuli are stored. The capsules are loaded through an insertion port (arrow) on the back of the device.