Fig. 3

Trial sequential analysis plots using different between-study variance estimators (\(\widehat{\tau }\) 2) for failed intubations comparing hyper-angulated video laryngoscopy and direct laryngoscopy. DL, DerSimonian-Laird estimator; HS, Hunter-Schmidt estimator; ML, Maximum-likelihood estimator; PM, Paule-Mandel estimator; REML, Restricted maximum-likelihood estimator; SJ, Sidik-Jonkman estimator