Table 1.

Sample characteristics

	Cases N = 384	Control N = 690	Statistics
Sex			χ2 = 20.8, df = 1, p < 0.001
Men, N (%)	236 (61.5)	324 (46.9)
Women, N (%)	148 (38.5)	366 (53.1)
Age, mean ± s.d.	31.8 ± 10.9	38.2 ± 13.4	F = 62.4, df = 1, p < 0.001
Years of education, mean ± s.d.	13.4 ± 3.9	15.2 ± 4.1	F = 48.9, df = 1, p < 0.001

Both patients and controls were recruited from 16 different sites. Eight participants had missing data on years of education, and one participant had missing data on age. All participants had data on sex. All participants were Caucasians.