It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
After you have conducted a comprehensive literature search and compiled a database of potentially useful studies, you now need to critically appraise the literature. You need to draw up appropriate criteria to decide which studies to include or exclude from your review, based on an unbiased appraisal of their strengths and limitations.
Cochrane Interactive Learning Resources
Modules 4-5 of Cochrane Interactive Learning have information on selecting studies, including how to assess the risk of bias. The Library is subscribing to Cochrane Interactive Learning.