Sample size
The estimation of the appropriate sample size is based on the corresponding Null hypotheses of the primary hypothesis, i.e. the assumption that VAL is inferior to conventional laryngoscopy in terms of first-attempt success rate, irrespective of the kind of blade in use. From clinical experience and previously published data, we assume an a-priori success rate of 90% across all groups. A clinically relevant difference between groups in this context is suggested at 5%, as is the accepted overall type-I error. Given that both Null hypotheses will be tested separately, the type-I error limit in each case is 2.5%. The desired statistical power is set to 90%. The Null hypotheses will be tested for non-inferiority using a one-sided Z test with unpooled variance. Based on these assumptions, the required sample size amounts to 3 * 824 = 2526 participants.