Skip to main content

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
  1. Reproduced from Harbour R, Miller J. A new system for grading recommendations in evidence based guidelines. BMJ (Clinical research ed 2001;323:334-6) with permission from BMJ Publishing Group Ltd. RCTs, Randomized controlled trials.
\