We will obtain the full texts of these four studies and on the basis of reading the full texts of these four studies, we will now synthesise the evidence. We will input the methods section and the results section of these studies to a GRADEPro data sheet and then we will analyse the results. 
Search and retrieval of results from Cochrane Database of Systematic Reviews
Alternatively, you can search and retrieve results from the Cochrane Database of Systematic Reviews. To do so, visit the following website, 
https://www.cochranelibrary.com/advanced-search/search-manager
... and start searching. We used a similar set of search terms we used for pubmed and we came up with the following search results: