2.2.3. Risk of Bias

The NICE public health guidance manual was used to assess the risk of bias for the included studies [21,22] (Table 2). Two reviewers performed the assessments independently, and the correlation was determined.

**Table 2.** Criteria to assess the risk of bias.


++ must meet at least six criteria indicated above. + must meet at least four criteria mentioned above. ++ denotes the low level of bias; + means the moderate level of bias; and − indicates a poor level of bias.
