"The Campbell Collaboration is an international research network that produces systematic reviews of the effects of social interventions in Crime & Justice, Education, International Development, and Social Welfare." These reviews are freely available on the Internet.
This free database includes more than 4,000 systematic reviews of public health interventions. In order to search and access these reviews you must first register, but registration is free.
To find meta analyses or systematic reviews, use the Advanced Search. Type your search terms in the search boxes. Then, scroll down to the Methodology box and choose either Systematic Review or Meta Analysis
Enter your search terms in the search box. The search results will be divided into three columns. The central column will contain systematic reviews, meta analyses, evidence based practice, etc.