Table 2.

Cohort studies: summary of risk factors for back pain episodes

Variable	Number of studies	Number of positive	Number of negative	Number not significant	Strength of association
Female sex	1	1	0	0	OR 2.1 (1.9, 2.5) [30]
Older Age	1	1	0	0	OR: (index 9 yr boy) 2.5 (1.5, 4.1) (13 yr boy), 3.2 (1.9, 5.3) (14 yr boy), 3.1 (1.8, 8.2) (15 yr boy), 3.0 (1.8, 5.2) (16 yr boy), 3.5 (1.9, 6.3) (17 yr boy), 2.4 (1.4, 4.1) (10 yr girl), 3.4 (2.1, 5.7) (11 yr girl), 4.6 (2.8, 7.5) (12 yr girl), 5.6 (3.4, 9.2) (13 yr girl), 5.4 (3.3, 8.9) (14 yr girl), 6.7 (4.1, 11.2) (15 yr girl), 6.7 (4.0, 11.3) (16 yr girl), 7.5 (4.2, 13.2) (17 yr girl) [30]

OR Odds ratio