Table 3 Subgroup analysis of the outcomes
Study group | Outcomes | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Â | Number of studies (n) | Number of participants (n) | test of association | Test of heterogeneity | ||||||
RR | 95%CI | p value | Model | p value | I2 | I2 test for subgroup differences (%) | p for the interaction between subgroup and treatment | |||
difficult intubation | ||||||||||
 Study design | ||||||||||
  Cohort | 3 | 5567 | 3.41 | 0.88–13.25 | 0.08 | RE | 0.14 | 50 | 23 | 0.25 |
  Case-control | 2 | 95,407 | 1.50 | 1.03–2.18 | 0.03 | RE | 0.08 | 67 | ||
 Position | ||||||||||
  Sniffing | 2 | 394 | 5.77 | 2.29–14.58 | 0.0002 | RE | 0.63 | 0 | 89.8 | 0.002 |
  Supine | 3 | 100,570 | 1.30 | 1.17–1.44 | < 0.00001 | RE | 0.59 | 0 | ||
difficult laryngoscopy | ||||||||||
 Study design | ||||||||||
  Cohort | 6 | 9111 | 1.85 | 1.31–2.63 | 0.0005 | RE | 0.08 | 49 | 67 | 0.08 |
  Case-control | 3 | 103,277 | 1.34 | 1.22–1.48 | < 0.00001 | RE | 0.87 | 0 | ||
 Position | ||||||||||
  Sniffing | 4 | 2210 | 2.0 | 0.97–4.15 | 0.06 | RE | 0.03 | 67 | 0 | 0.42 |
  Supine | 5 | 110,178 | 1.47 | 1.23–1.76 | < 0.0001 | RE | 0.22 | 30 | ||
Mallamp-ati ≥ 3 | ||||||||||
 Study design | ||||||||||
  Cohort | 9 | 4189 | 1.9 | 1.12–3.21 | 0.02 | RE | < 0.00001 | 85 | 0 | 0.6 |
  Case-control | 3 | 1489 | 1.62 | 1.27–2.08 | 0.0001 | RE | 0.61 | 0 |  |  |