Reviews of evidence

The preceding chapters have focused on the generation of scientific evidence using epidemiological studies. Here the emphasis is on bringing together evidence (evidence synthesis) to inform future research and health policies. The chapter considers levels and quality of scientific evidence and describes in detail how to conduct a systematic review. It reviews the ways of summarizing and evaluating evidence from epidemiological studies. Summary of evidence is needed in everyday clinical practice and for public health. We live in a time of information overload, and it is impossible to read all the available scientific journals, even on a narrow scientific topic. Simply using search terms such as ‘cancer’ will result in millions of results in Google Scholar or PubMed (a service of the US National Library of Medicine®) database. Given the ever-increasing volume of medical literature and time constraints, summary of evidence plays a big role in decision-making.