2.3 Test procedure
Sniffin’ Sticks Olfactory Identification test: The test comprises 16 felt-tip pen-like d-evices; only one olfactory pen cap can be opened at a time. The pen tip was placed appr-oximately 2 cm under the middle of the subject’s double nostrils and did not touch the su-bject’s skin. The time for the subject to smell each pen shall not exceed 2–3 seconds, with an interval of about 30 seconds. After presenting a stick, the subject was provided with f-our odor descriptors to select the option that could best describe the presented odor. Even if subjects were uncertain about the odor, they were required to use the exclusion method to make a choice. The test was repeated successively until all 16 odors were presented.