Mean age (y) (SD) (Q1–Q3)§ | 41.6 (10.0) (33.0–48.0) | 40.2 (8.5) (37.0–44.0) | 44.5 (5.7) (42.0–48.0) | 37.4 (8.1) (31.0–42.0) | 0.02* |
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Males (n) (%) | 21 (81) | 18 (58) | 13 (59) | 10 (40) | 0.03† |
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Mean body mass index (SD) (Q1–Q3)§ | 25.8 (3.3) (23.2–27.5) | 24.6 (4.0) (21.2–28.4) | 25.5 (4.6) (22.1–29.1) | 24.7 (4.2) (21.3–27.1) | 0.66‡ |
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Mean days of absence from work before entry in study (SD) (Q1–Q3)§ | 38.3 (13.4) (29.0–44.0) | 39.6 (12.7) (30.0–45.0) | 44.8 (18.6) (33.0–55.0) | 43.8 (13.3) (30.0–55.0) | 0.35* |
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Mean Oswestry score (SD) (Q1–Q3)§ | 29.8 (14.7) (18.0–42.0) | 33.7 (14.6) (26.0–42.0) | 30.0 (18.0) (16.0–38.0) | 31.1 (15.6) (20.0–42.0) | 0.77‡ |
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Mean Sickness Impact Profile score (SD) (Q1–Q3)§ | 15.8 (8.9) (10.0–21.0) | 15.2 (6.6) (10.0–21.0) | 13.2 (8.9) (6.0–18.0) | 13.9 (8.7) (8.0–16.0) | 0.44* |
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Mean pain level (McGill-Melzack questionnaire) (SD) (Q1–Q3)§ | 22.9 (14.2) (13.0–28.0) | 28.5 (18.4) (14.0–43.0) | 22.9 (19.5) (8.0–30.0) | 27.0 (27.7) (12.0–35.0) | 0.42* |
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Mean work APGAR satisfaction (SD) (Q1–Q3)§ | 11.3 (2.4) (10.0–13.0) | 11.1 (2.2) (10.0–12.0) | 10.9 (3.1) (8.0–14.0) | 11.1 (2.7) (9.0–14.0) | 0.94* |
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Mean income (1991 Canadian $) (Q1–Q3)§ | 31313 (25383–38196) | 29940 (24395–32217) | 27234 (25549–29402) | 26174 (24786–26889) | – |