2.4.1 Odor familiarity survey
The familiarity of 121 odors was investigated in 100 volunteers (aged 18–65 years). Based on Niklassen et al.’s study22, we developed an odor familiarity questionnaire co-ntaining 121 kinds of odors. The questionnaire included basic information of the volunte-ers: name, gender, age, contact details, and occupation (strict measures were taken to ens-ure that the privacy and personally identifiable information of volunteers were not expos-ed during the research process, and the names of volunteers were hidden and replaced by numbers only). According to the familiarity with the 121 common odors provided in the questionnaire, we used a Likert-type scale for the volunteers to score using an online or paper questionnaire (the content of the online and paper questionnaires were similar). T-he scale ranged from 1 to 5, for which 1 is not familiar, and 5 is highly familiar. If the v-olunteers scored 4 or 5 on an odor, they were considered ”familiar” with the odor. The n-umber of ”familiar” volunteers with an odor among 100 volunteers was the final familia-rity score of the odor.