Evidence synthesis uses formal, explicit, and rigorous methods to bring together the findings of research already completed, to provide an account of the totality what is known from that pre-existing research.
Different users of research with varying perspectives may have different questions they wish research to address. This has led evidence synthesis methods to address a wide range of research questions including the prevalence of different phenomena, the evaluation of the impact of an intervention, the processes by which an intervention has an impact, and the meaning of different experiences for people. The findings of evidence synthesis can also help to identify research gaps, prioritize research needs, encourage quality and completeness of execution and reporting of research, avoid duplication, and reduce wastage of research effort.
With the breadth of questions that evidence syntheses address, the extent of ‘work done’ by a synthesis, the extent of a ‘research problem’ that a review attempts or manages to address, as well as the depth of analysis and how rapidly they are undertaken also vary. Given this variation, the development of standards for the execution and reporting of evidence using several types of synthesis are helpful in identifying the standards of quality, rigour and relevance that should be required for different types of evidence syntheses.