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Table 3 Subgroup analysis of the outcomes

From: The association of body mass index with difficult tracheal intubation management by direct laryngoscopy: a meta-analysis

Study group Outcomes
  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   
  1. CI confidence interval, RE random-effect model, RR risk ratio, I2 a test for heterogeneity, I2 > 50% indicates substantial heterogeneity