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Table 2 Covariates and outcome of adult bicycle traffic accident helmet users and nonusers before and after propensity score matching (1:1 matching)

From: The protective effect of helmet use in motorcycle and bicycle accidents: a propensity score–matched study based on a trauma registry system

  Before matching After matching
Covariates Helmet use
Yes n = 76
Helmet use
No n = 647
Odds ratio
(95%CI)
P Helmet use
Yes n = 76
Helmet use
No n = 76
Mean
Difference
Standardized
Difference
Age 48.8 ± 13.7 63.1 ± 15.6 <0.001 48.8 ± 13.7 48.7 ± 13.8 0.09211 0.67(%)
Sex
 Male 60(78.9) 355(54.9) 3.1(1.74–5.47) <0.001 60(78.9) 60(78.9) 1.0(0.46–2.18) 0.00(%)
 Female 16(21.1) 292(45.1) 0.3(0.18–0.58) <0.001 16(21.1) 16(21.1) 1.0(0.46–2.18) 0.00 (%)
Comorbidity
 DM 3(3.9) 86(13.3) 0.3(0.08–0.87) 0.019 3(3.9) 3(3.9) 1.0(0.20–5.12) 0.00 (%)
 HTN 12(15.8) 221(34.2) 0.4(0.19–0.68) 0.001 12(15.8) 12(15.8) 1.0(0.42–2.39) 0.00 (%)
 CAD 1(1.3) 22(3.4) 0.4(0.05–2.85) 0.498 1(1.3) 1(1.3) 1.0(0.06–16.29) 0.00 (%)
 CHF 0(0.0) 4(0.6) 1.000 0(0.0) 0(0.0)
 CVA 0(0.0) 28(4.3) 0.063 0(0.0) 0(0.0)
 ESRD 0(0.0) 2(0.3) 1.000 0(0.0) 0(0.0)
Outcome
GCS 14.5 ± 2.4 14.2 ± 2.4 0.303 14.5 ± 2.4 14.2 ± 2.6 0.538
 ≤ 8 3(3.9) 34(5.3) 0.7(0.22–2.47) 0.788 3(3.9) 4(5.3) 0.7(0.16–3.42) 1.000
 9–12 0(0.0) 31(4.8) 0.065 0(0.0) 2(2.6) 0.497
 ≥ 13 73(96.1) 582(90.0) 2.7(0.83–8.87) 0.085 73(96.1) 70(92.1) 2.1(0.50–8.67) 0.494
AIS ≥ 3, n (%)
 Head/Neck 9(11.8) 166(25.7) 0.4(0.19–0.80) 0.008 9(11.8) 14(18.4) 0.6(0.24–1.47) 0.258
 Face 0(0.0) 1(0.2) 1.000 0(0.0) 0(0.0)
 Thorax 4(5.3) 33(5.1) 1.0(0.36–3.00) 1.000 4(5.3) 3(3.9) 1.4(0.29–6.26) 1.000
 Abdomen 0(0.0) 7(1.1) 1.000 0(0.0) 0(0.0)
 Extremity 20(26.3) 208(32.1) 0.8(0.44–1.29) 0.301 20(26.3) 19(25.0) 1.1(0.52–2.22) 0.853
ISS, median (IQR) 5.5(4–9) 9(4–10) 0.029 5.5(4–9) 7(4–10) 0.808
 < 16 68(89.5) 523(80.8) 2.0(0.94–4.30) 0.065 68(89.5) 63(82.9) 1.8(0.68–4.51) 0.240
 16–24 5(6.6) 88(13.6) 0.4(0.18–1.14) 0.084 5(6.6) 11(14.5) 0.4(0.14–1.26) 0.113
 ≥ 25 3(3.9) 36(5.6) 0.7(0.21–2.32) 0.788 3(3.9) 2(2.6) 1.5(0.25–9.37) 1.000
Hospital LOS (days) 7.0 ± 9.5 8.9 ± 10.2 0.116 7.0 ± 9.5 6.7 ± 6.4 0.858
ICU
 Patients, n (%) 9(11.8) 139(21.5) 0.5(0.24–1.01) 0.049 9(11.8) 11(14.5) 0.8(0.31–2.04) 0.631
 < 16 4(5.3) 38(5.9) 0.9(0.31–2.57) 1.000 4(5.3) 1(1.3) 4.2(0.46–38.17) 0.367
 16–24 2(2.6) 69(10.7) 0.2(0.05–0.94) 0.026 2(2.6) 8(1.1) 0.2(0.05–1.12) 0.050
 ≥ 25 3(3.9) 32(4.9) 0.8(0.24–2.64) 1.000 3(3.9) 2(2.6) 1.5(0.25–9.37) 1.000
 ICU LOS (days) 11.0 ± 20.1 7.4 ± 9.5 0.612 11.0 ± 20.1 4.3 ± 2.3 0.346
Mortality 4(5.3) 24(3.7) 1.4(0.49–4.27) 0.524 4(5.3) 3(3.9) 1.3(0.30–5.96) 0.706
  1. CI confidence interval, BMI body mass index, DM diabetes mellitus, HTN hypertension, CAD coronary artery disease, CHF congestive heart failure, CVA cerebral vascular accident, ESRD end-stage renal disease, BAC blood alcohol concentration, GCS Glasgow Coma Scale, AIS Abbreviated Injury Scale, ISS injury severity score, IQR interquartile range, LOS length of stay, ICU intensive care unit