You might ask yourself, is this step really necessary? Can’t I just read every study and summarize the results in my final report? You could, but then you wouldn’t be conducting a systematic review. To systematically weigh and evaluate the existing evidence, you need to put all of your information into a standard format.
That way, you can create informative tables and graphs that make it easy to summarize and compare information from different studies. And of course, any kind of meta-analysis is impossible without this step.
But data extraction does more than just organize and standardize the results of your studies. It forces you to really look at the research.