Table 2.

NICE rating system for methodological quality of studies using methodological checklists (NICE, 2007).

++	All or most of the criteria have been fulfilled. Where they have not been fulfilled the conclusions of the study or review are thought very unlikely to alter
+	Some of the criteria have been fulfilled. Those criteria that have not been fulfilled or not adequately described are thought unlikely to alter the conclusions
−	Few or no criteria fulfilled. The conclusions of the study are thought likely or very likely to alter