Table 4 Levels of evidence
From: A systematic review of the role of videolaryngoscopy in successful orotracheal intubation
1++ | RCTs with a very low risk of bias (or high quality meta-analyses, systemic reviews of RCTs) |
1+ | RCTs with a low risk of bias (or well conducted meta-analyses, systematic reviews of RCTs) |
1- | RCTs with a high risk of bias (or meta-analyses, systematic reviews or RCTs) |
2++ | High quality case–control or cohort studies with a very low risk of confounding/bias/chance and a high probability that the relationship is causal (or High quality systematic reviews of case–control or cohort studies) |
2+ | Well conducted case–control or cohort studies with a low risk of confounding/bias/chance and a moderate probability that the relationship is causal |
2- | Case–control or cohort studies with a high risk of confounding/bias/chance and a significant risk that the relationship is not causal |
3 | Non-analytic studies, eg. Case reports, case series |
4 | Expert opinion |