|Evidence level of systematic reviews|
|Score||Source of evidence|
|1++||High quality meta analyses or systematic reviews of RCT’s|
|1+||Well conducted meta analyses or systematic reviews of RCT’s|
|1-||Meta analyses or systematic reviews of RCT’s|
|2++||High quality systematic reviews of case control or cohort studies|
|2+||Well conducted case control or cohort studies with low risk of bias|
|2-||Case control or cohort studies with high risk of bias|
|3||Case reports or case series|
|4||Expert opinion or formal consensus|
From Scottish Intercollegiate Guidelines Network .
McNeill et al.
McNeill et al. BMC Public Health 2012 12:955 doi:10.1186/1471-2458-12-955