Table 2

Z-score of grade-point average as a risk factor for bipolar disorder

Standardised grade category Population n (%) Bipolar disorder n (%) Incidence per 100 000 person-years (95% CI) Crude hazard ratio (95% CI) Adjusted hazard ratioa (95% CI)
a. Adjusted analysis includes adjustment for gender, paternal and maternal age > 40 at birth, highest parental education, spring birth and socioeconomic status.
< -2 20 517 (2.9) 13 (4.7) 6.68 (3.88-11.50) 1.86 (1.06-3.28) 1.96 (1.07-3.56)
-2 to -1 104 707 (14.7) 37 (13.4) 3.69 (2.67-5.09) 1.03 (0.72-1.47) 1.16 (0.81-1.68)
-1 to +1 461 628 (64.8) 160 (57.2) 3.60 (3.08-4.21) 1.00 1.00
+1 to +2 115 981 (16.3) 56 (20.3) 5.16 (3.97-6.70) 1.42 (1.05-1.93) 1.24 (0.90-1.71)
> +2 9 427 (1.3) 12 (4.3) 13.83 (7.85-24.35) 3.79 (2.11-6.82) 3.34 (1.82-6.11)