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Table 2 Comparison of baseline characteristics between participants with LBP who did (FU) and did not (NFU) follow-up at 3, 6, 9 and 12 months

From: Cohort profile: why do people keep hurting their back?

Characteristic 3 months 6 months 9 months 12 months
Summary statistics P-value Summary statistics P-value Summary statistics P-value Summary statistics P-value
FU (N = 98) NFU (N = 35) FU (N = 89) NFU (N = 44) FU (N = 84) NFU (N = 49) FU (N = 92) NFU (N = 41)
Demographic, health & function
Age (years) 28 (22–34) 24 (20–32) 0.074 27 (22–34) 26.5 (20.5–33.5) 0.362 27.5 (22.5–34) 25 (21–34) 0.264 27 (22.5–35) 25 (20–31) 0.090
Sex (% female) 48.0 62.9 0.130 49.4 56.8 0.423 50.0 55.1 0.570 51.1 53.7 0.784
Height (m)†* 1.73 (0.09) 1.70 (0.09) 0.078 1.73 (0.09) 1.71 (0.09) 0.173 1.73 (0.09) 1.72 (0.09) 0.615 1.73 (0.09) 1.71 (0.09) 0.507
Weight (kg)‡* 73 (63–82) 72 (56–85) 0.746 73 (62–82) 73.5 (60.5–84.5) 0.815 72.5 (62.5–82.5) 74 (61–84) 0.744 71.5 (60.5–81.5) 75 (62–85) 0.680
BMI (kg/m2) 24.0 (21.4–26.3) 25.2 (21.0–27.7) 0.409 24.0 (21.4–26.3) 24.1 (21.7–27.5) 0.449 24.0 (21.8–26.3) 23.9 (21.1–27.2) 0.961 23.9 (21.4–26.1) 25.9 (21.2–27.4) 0.313
Comorbidity (yes, %) 41.8 54.3 0.204 42.7 50.0 0.426 40.5 53.1 0.159 0.5 41.5 0.572
Previous LBP (yes, %) 92.9 88.6 0.429 92.1 90.9 0.809 91.7 91.8 0.973 92.4 90.2 0.678
Healthcare utilization (yes, %) 18.4 23.5 0.514 20.2 18.6 0.826 21.4 16.7 0.508 19.6 20.0 0.954
Medication utilization (yes, %) 18.8 32.1 0.152 21.1 25.0 0.650 19.7 26.8 0.390 16.7 34.3 0.040
Function (LBOS) 48.4 (11.2) 42.7 (10.8) 0.012 48.3 (10.7) 44.1 (12.2) 0.048 48.2 (10.5) 44.6 (12.4) 0.077 48.1 (11.0) 44.1 (11.7) 0.060
Outcome
Pain (NRS) 5 (3–6) 6 (5–7) 0.019 5 (3–6) 6 (4–7) 0.078 5 (3–7) 5 (4–7) 0.506 5 (3–6.5) 6 (4–7) 0.147
Disability (RMDQ) 6 (3–9) 7 (4–11) 0.140 6 (3–9) 6.5 (4–10.5) 0.293 6 (4–9) 6 (4–10) 0.613 6 (4–9) 7 (4–10) 0.257
Psychological
Depressive symptoms (CES-D) 11 (7–17) 16 (10–25) 0.003 10 (7–17) 16 (10–22) 0.008 10 (7–18) 15 (10–22) 0.004 10 (7–18) 15 (11–23) 0.017
Pain catastrophizing (PCS) 10 (6–16) 19 (7–26) 0.057 10 (6–16) 13 (7–26) 0.125 10 (6–16) 14 (7–26) 0.106 10 (6–16) 17 (9–26) 0.019
Fear avoid.-work (FABQ-W) 11 (2–17) 15 (6–22) 0.136 12 (2–17) 12 (3–24) 0.223 12 (3–17) 13 (4–23) 0.144 12 (4–17) 10 (0–23) 0.960
Fear avoid.-activity (FABQ-PA) 14.7 (5.5) 14.9 (5.4) 0.835 14.7 (5.3) 14.8 (5.8) 0.944 14.6 (5.6) 15.0 (5.4) 0.686 14.8 (5.4) 14.7 (5.8) 0.926
Pain self-efficacy (PSEQ) 48 (40–53) 41 (32–48) 0.008 48 (40–52) 44 (32–48) 0.021 48 (40–53) 44 (32–48) 0.009 47 (40–53) 45 (32–48) 0.047
Social
Marital status (not married/cohabitating, %) 65.3 58.8 0.498 64.0 62.8 0.888 64.3 62.5 0.837 63.0 65.0 0.830
Edu. level (secondary school/below, %) 24.5 26.5 0.818 24.7 25.6 0.915 23.8 27.1 0.676 25.0 25.0 1.000
Empl. status (unemployed, %) 25.5 14.7 0.195 25.8 16.3 0.219 25.0 18.8 0.410 20.7 27.5 0.388
Job satisfaction (NRS) 4.3 (1.2) 3.8 (1.1) 0.070 4.3 (1.2) 3.9 (1.2) 0.092 4.3 (1.2) 3.8 (1.1) 0.025 4.3 (1.2) 3.8 (1.1) 0.044
Job skill discretion (JCQ) 38 (32–42) 34 (28–40) 0.249 38 (32–42) 34 (30–40) 0.213 38 (32–42) 34 (30–39) 0.148 38 (32–41) 36 (32–40) 0.470
Job decision-making authority (JCQ) 40 (32–44) 36 (28–42) 0.081 40 (32–44) 36 (28–44) 0.136 40 (36–44) 36 (28–40) 0.026 40 (32–44) 36 (28–44) 0.254
Job demands (JCQ) 32 (27–36) 33 (31–38) 0.096 32 (27–36) 33 (30–38) 0.068 32 (27–36) 33 (29–38) 0.214 32 (29–36) 33 (26–38) 0.922
Job decision latitude (JCQ) 76 (66–86) 70 (56–80) 0.152 76 (67–86) 70 (62–82) 0.172 77 (68–86) 70 (60–80) 0.058 76 (66–86) 74 (62–82) 0.353
Co-worker support (JCQ) 12 (12–14) 12 (11–12)  < 0.001 12 (12–14) 12 (11–12) 0.002 13 (12–14) 12 (11–12)  < 0.001 12 (12–14) 12 (12–13) 0.190
Supervisor support (JCQ) 12 (12–15) 12 (11–14) 0.341 12 (12–15) 12 (11–14) 0.411 12 (12–16) 12 (11–13) 0.122 12 (11–16) 12 (11–13) 0.530
Job insecurity (JCQ)‡∆ 5 (4–7) 6 (5–8) 0.156 5 (4–7) 6 (5–7) 0.088 5 (4–7) 6 (5–8) 0.046 5 (4–7) 5 (5–7) 0.308
Sick days over last 12 months‡* 2 (0–4) 2 (0–5) 0.618 2 (0–4) 2 (0–5) 0.711 2 (0–4) 2 (0–5) 0.803 2 (0–4) 2 (0–5) 0.975
Sickness benefits for LBP (yes, %) 1.3 3.6 0.439 1.4 2.8 0.621 1.5 2.4 0.732 0.0 5.7 0.041
Impending compensation (yes, %) 6.3 17.9 0.072 7.0 13.9 0.250 7.6 12.2 0.425 4.2 20.0 0.008
Behavioural
Sleep quality (PSQI) 9.0 (3.3) 10.0 (3.2) 0.215 9.0 (3.4) 9.7 (3.1) 0.337 9.0 (3.5) 9.6 (3.0) 0.334 9.2 (3.5) 9.1 (2.9) 0.828
Alcohol use/related problems (AUDIT) 3 (2–6) 3 (1–7) 0.996 3 (2–6) 3 (1–7) 0.778 3 (1–6) 3 (2–8) 0.617 3 (2–6) 3 (1–8) 0.742
Previous/current smoker (yes, %) 35.7 38.2 0.792 36.0 37.2 0.888 34.5 39.6 0.561 35.9 37.5 0.858
Current smoker (yes, %) 6.1 11.8 0.284 6.7 9.3 0.602 6.0 10.4 0.351 5.4 12.5 0.159
Vig. phys. activity days/week (IPAQ)‡* 2 (0–3) 1 (0–3) 0.783 2 (0–3) 2 (0–4) 0.312 2 (0–3) 2 (0–3) 0.606 2 (0–3) 1 (0–2) 0.233
Vig. phys. activity time/day (min, IPAQ)‡* 20 (0–60) 20 (0–60) 0.728 18 (0–60) 30 (0–60) 0.263 20 (0–60) 25 (0–60) 0.700 28 (0–60) 0 (0–60) 0.575
Mod. phys. activity days/week (IPAQ)‡* 2 (1–4) 2 (0–4) 0.979 2 (1–4) 2 (0–4) 0.743 2 (1–4) 2 (0–4) 0.874 2 (1–4) 2 (0–4) 0.228
Mod. phys. activity time/day (min, IPAQ)‡* 30 (0–60) 30 (0–30) 0.082 30 (0–60) 23 (0–30) 0.070 30 (0–60) 30 (0–35) 0.113 30 (0–60) 30 (0–45) 0.233
Days/week walking for ≥ 10 min (IPAQ)‡* 6 (4–7) 6 (4–7) 0.806 6 (4–7) 6 (3–7) 0.594 6 (4–7) 6 (4–7) 0.747 6 (4–7) 6 (4–7) 0.729
Walking time/day (min, IPAQ)‡* 30 (18–60) 30 (20–90) 0.158 30 (20–45) 35 (20–75) 0.118 25 (15–40) 45 (20–75) 0.023 25 (20–45) 48 (20–60) 0.076
Sitting time/day (min, IPAQ)†* 430.6 (174.8) 385.0 (211.3) 0.298 429.4 (173.6) 394.3 (209.9) 0.401 437.3 (176.1) 381.3 (198.6) 0.166 428.7 (173.6) 393.5 (212.5) 0.410
  1. Baseline variable (characteristic) summary statistics (mean [SD], median [IQR] or percentage) compared between low back pain (LBP) participants who did (FU) and did not follow-up (NFU), separately at 3, 6, 9 (for laboratory-based measures) and 12 (questionnaire measures) month time-points using t tests (continuous data, normally distributed), Mann–Whitney U tests (continuous data, not normally distributed) or Chi squared tests (categorical data). Edu. education, Empl employment, Vig vigorous, Mod moderate, min minute. Refer to Table 1 for other abbreviations.
  2. *If a participant provided a range of values in response to a question (e.g., 30–60 min), the average was calculated for analysis purposes.
  3. Participants who answered “other” to question 25 of the Job Content Questionnaire were removed prior to analysing the “job insecurity” scale.