Table 1 Univariate logistic regression and multivariate logistic analysis showing the association of variables with difficult laryngoscopy

 I

ref.

ref.

 II

2.346 (1.455, 3.784)

<0.001

1.428 (0.812, 2.509)

0.216

 III

14.406 (8.447, 24.569)

<0.001

4.114 (2.114, 8.005)

<0.001

 I/II

ref.

ref.

 III

1.943 (1.255, 3.007)

0.003

1.016 (0.594, 1.737)

0.955

 IV

4.644 (3.077, 7.009)

<0.001

2.461 (1.411, 4.292)

0.002

 male

ref.

ref.

 female

0.325 (0.223, 0.473)

<0.001

0.285 (0.174, 0.466)

<0.001

 <12

ref.

ref.

 ≥12

0.030 (0.018, 0.051)

<0.001

0.044 (0.025, 0.077)

<0.001

 <36

ref.

ref.

 36-51

4.925 (1.512, 16.044)

0.008

2.891 (0.795, 10.521)

0.107

 ≥52

12.333 (3.885, 39.157)

<0.001

5.113 (1.430, 18.286)

0.012

 <18.5

ref.

ref.

 [18.5,24)

0.947 (0.504, 1.780)

0.866

1.464 (0.659, 3.250)

0.349

 [24,27)

1.325 (0.677, 2.595)

0.411

1.766 (0.726, 4.295)

0.21

 [27-30)

1.979 (0.946, 4.138)

0.07

4.172 (1.541, 11.299)

0.005

 ≥30

0.754 (0.206, 2.753)

0.669

1.587 (0.301, 8.360)

0.586

 <65

ref.

ref.

 [65,78)

0.274 (0.182, 0.414)

<0.001

0.391 (0.226, 0.678)

0.001

 ≥78

0.151 (0.090, 0.254)

<0.001

0.254 (0.130, 0.497)

<0.001

 <40

ref.

ref.

 ≥40

0.181 (0.123, 0.266)

<0.001

0.554 (0.342, 0.897)

0.016

 <60

ref.

ref.

 60-67

2.561 (1.757, 3.733)

<0.001

1.495 (0.917, 2.436)

0.107

 >67

6.985 (3.937, 12.391)

<0.001

4.525 (1.918, 10.672)

0.001