Not all studies are trustworthy. In order for your systematic review to represent the best possible evidence, your team must critically appraise each study thoroughly before it is included. The criteria by which you assess included studies should be clearly outlined in your report. You should also maintain a record of which studies have been left out, and the grounds for which they were excluded.
Once multiple team members have screened the entire list of references, you will be left with a core group of studies to be included in your review. The next step is to extract the data from each of the studies in order to synthesize their results. The extraction process should be tracked using a standardized data extraction form (see examples below). Data can also be coded for computer analysis. For more information about data extraction, check out this subject guide by the Himmelfarb Health Sciences Library at George Washington University: