Perception of odour intensity. a c, Thresholds for pentadecalactone (a), vanillin (b), and isovaleric acid (c) for different demographic groups. A two-tailed Mann–Whitney test (*p<0.05; **p<0.01; ***p<0.001; n.s.: not significant) was performed to test the differences for statistical significance. Mean±S.D. are shown. d h, Differences in intensity rank of stimuli. Only statistically significant differences are shown. The test for statistical significance was a two-tailed Mann–Whitney test with a sequential Bonferroni correction called the Holm’s method to correct for multiple comparisons (p<0.0082). Odour names are labelled according to odour concentration: grey: low; black: high; (Ns: < 35 years: 195; > 35 years: 196; Women: 210; Men: 181; Asians: 31; African-Americans: 97; Caucasians: 178; Perfume users: 267; Non-perfume users: 112). Subjects were divided by age according to the median of 34.6 years, which is rounded to 35 years for labeling the figure.