Table 5 Overall rating of internal and external validity in modified Graphical Appraisal Tool for Epidemiological studies (GATE)

++

All or most of the checklist criteria have been fulfilled, where they have not been fulfilled the conclusions are very unlikely to alter.

+

Some of the checklist criteria have been fulfilled, where they have not been fulfilled, or not adequately described, the conclusions are unlikely to alter.

-

Few or no checklist criteria have been fulfilled and the conclusions are likely or very likely to alter.