People are bad at evaluating their own olfactory abilities, overestimating and underestimating them

Why We Both Trust and Mistrust Our Sense of Smell. Ophelia Deroy. Chp 3 in Theoretical Perspectives on Smell, Andreas Keller and Benjamin D. Young, Eds. Routledge, 2023. DOI: 10.4324/9781003207801

3.2 Trusting Our Sense of Smell: One Problem or Many?

Let’s go back to the initial claim, exemplified by the medical quote above, that people are bad at evaluating their own olfactory abilities. Besides such anecdotal evidence, this claim has been tested in controlled and systematic ways: subjects are asked to assess their olfactory capacities, before their actual capacities are measured using standardised test.

When such tests have been conducted, they found no correlation between subjective and objective olfactory ratings,1 or only a poor one. In what is perhaps the largest scale study, 2 involving more than 6,000 patients who were coming to a smell clinic, self-ratings of “good or excellent” sense of smell could predict at 64% the fact that one had a normal sense of smell, while almost 30% (355 subjects) of anosmic patients judged their ability to smell as at least “average”. Repeatedly, reports show that people are often unaware that their olfactory sense is missing—a tendency which also increases with age (Nordin et al. 1995; Shu et al. 2009; Oleszkiewicz et al. 2020; Oleszkiewicz & Hummel 2019). In another study, White and Kurtz (2003) asked young and old individuals to determine whether their sense of smell was in the lower, middle/average tier, or upper tier compared to the rest of the population, and compared their subjective evaluations with their actual score on the Detection, Discrimination, Identification test.

Their results showed that young people tended to judge their sense of smell as less good than what it was, while older people judged their sense of smell to better than in reality. Most participants over-estimated their sense of smell, and very few would provide assessments in line with their performance on the test.

Though such statistics can be surprising, they ask a more philosophical question: Why even expect that people could tell how good their sense of smell is? Do we after all, expect people to know how good their memory or digestion are, or just have a rough idea when things go very wrong?

The literature on olfactory self-evaluation is here largely coloured by the existence of “olfactory anosognosia”: cases where olfactory loss gets unnoticed, and people who can’t smell still think they can. For people with normal olfactory capacities however, the problem is that of a bias in their evaluation of how good their sense of smell is: they can be either over-confident and think their sense of smell is better than it is or underconfident and think their sense of smell is worse that it is.