Table 4 Level of certainty definitions used for assessment of summary conclusions (adapted from [59, 60])

High

The relationships investigated included evidence from at least two, level I studies with a summary conclusion revealing consistent results. The summary conclusion is unlikely to be strongly affected by future studies.

Moderate

The relationships investigated included evidence from either of the following: (i) only one, level I study and level II and/or level III/IV studies with a consistent summary conclusion; (ii) at least two, level II studies with a consistent summary conclusion; or (iii) level I and/or level II studies with an inconsistent summary conclusion. As more information becomes available, the summary conclusion could change.

Low

The relationships investigated included evidence from either: (i) only one, level II study and level III/IV studies with consistent or inconsistent results; or (ii) level III/IV studies only with consistent or inconsistent results. More information is needed to be certain of the summary conclusion.

Insufficient

The relationships investigated included evidence from only one study (regardless of level of evidence) or with an unknown summary conclusion, indicating < 5 relationships were investigated. More research is needed to establish a relationship summary conclusion.