The study, spanning 20 years, involved 8179 men and women aged 30 years whose IQ was tested at age 10 years. Vegetarians were more likely to be female, to be of higher occupational social class and to have higher academic or vocational qualifications than non-vegetarians, although these differences were not reflected in their annual income, which was similar to that of non-vegetarians.
Higher IQ at the age of 10 years was associated with an increased likelihood of being vegetarian at the age of 30. This relation was partly accounted for by better education and higher occupational social class, but it remained statistically significant after adjusting for these factors.