Searching for existing evidence syntheses on a topic related to your own research question can be a good place to start your evidence synthesis process. These evidence syntheses may provide a model for approaching your own review of the literature, including recommended search strategies and resources. Below are links to online libraries of evidence syntheses and evidence documents for health and other areas of policy-making.
Just because a review has been published, it does not imply that the review was rigorous, reproducible or exhaustive. There are a number of criteria by which you can assess the quality of an evidence synthesis. Below are the two most common tools used for this purpose.