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Table 1 Comparison of effect estimate by various subgroups

From: Seatbelt use and risk of major injuries sustained by vehicle occupants during motor-vehicle crashes: a systematic review and meta-analysis of cohort studies

Grouping variable

Subgroup

Numb. of studies

Sample

RR (95% CI)

Prediction intervals

Tau2

I2 (95%CI)

H (95%CI)

P-value for heterogeneity

P-value Egger’s test

P-value difference in subgroups

Overall (any injury)

–

11

38,662,538

0.47 (0.28–0.80)

0.07–3.27

0.669

99.9 (99.9–99.9)

34.7 (33.2–36.4)

< 0.0001

0.361

NA

By injury site

Head

6

32,964,587

0.49 (0.22–1.08)

0.03–8.65

0.910

99.3 (99.1–99.4)

11.6 (10.1–13.4)

< 0.0001

0.046

0.090

Spinal

7

5,281,081

0.56 (0.37–0.84)

0.15–2.01

0.206

93.1 (88–96)

3.8 (2.9–5.0)

< 0.0001

0.328

Facial

2

409,016

0.75 (0.40–1.43)

–

0.207

96.9

–

< 0.0001

–

Neck

2

855

0.69 (0.07–6.44)

–

1.761

56.6

–

0.129

–

Thoracic

2

855

0.96 (0.74–1.25)

–

0.0

0.0

–

0.754

–

Abdomen

2

4621

0.93 (0.84–1.04)

–

0.0

0.0

–

0.912

–

Upper limb

1

766

1.05 (0.83–1.34)

–

–

–

–

–

–

Lower limb

1

766

0.77 (0.58–1.04)

–

–

–

–

–

–

By crash type

Motor vehicle collision

5

5,692,713

0.64 (0.46–0.89)

0.19–2.17

0.119

98.8 (98–99)

9.0 (7.4–10.8)

< 0.0001

0.670

0.001

Rollover

3

3,276,677

0.43 (0.20–0.93)

0.0–963.4

0.465

99.2 (99–99.6)

11.4 (9.1–14.3)

< 0.0001

0.268

Multiple

3

3447

0.37 (0.30–0.44)

0.11–1.27

0.0

0.0 (0.0–90)

1.0 (1.0–3.1)

0.506

0.025

Front

1

18,296,847

0.18 (0.18–0.19)

–

–

–

–

–

–

Side

1

8,571,748

0.15 (0.14–0.15)

–

–

–

–

–

–

Rear

1

2,821,106

0.09 (0.08–0.09)

–

–

–

–

–

–

By study sample size

< median (6128)

5

4662

0.51 (0.20–1.30)

0.02–12.46

0.783

94.5 (90–97)

4.3 (3.2–5.8)

< 0.0001

0.121

0.594

≥ median (6128)

6

38,657,876

0.45 (0.23–0.86)

0.04–5.10

0.659

99.9 (99.9–99.9)

48.7 (46.3–51.2)

< 0.0001

0.340

By study type

Hospital

3

6189

0.39 (0.01–1.72)

0.0–5025

1.079

61.1 (0–89)

1.6 (1.0–3.0)

0.077

0.038

0.967

Patient databases

8

38,656,349

0.48 (0.27–0.84)

0.06–3.88

0.648

99.9 (99.9–99.9)

40.6 (38.6–42.6)

< 0.0001

0.452

Publication year

Before 2010

3

5,270,440

0.36 (0.33–0.38)

0.22–0.57

0.0

0.0 (0.0–90)

1.0 (1.0–3.1)

0.530

0.036

0.269

On or after 2010

8

33,392,098

0.54 (0.30–0.98)

0.06–4.75

0.697

99.9 (99.9–99.9)

41.4 (39.4–43.4)

< 0.0001

0.388

  1. NB: Absent predictive intervals could not be estimated due to inadequate number of studies (less than 3); absent I2 confidence intervals could not be estimated due to degrees of freedom less than 2 and Egger’s test was inestimable for groups with less than 3 studies
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BMC Public Health

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