Summarizing study characteristics and preparing for synthesis

Synthesis is a process of bringing together data from a set of included studies with the aim of drawing conclusions about a body of evidence. This will include synthesis of study characteristics and, potentially, statistical synthesis of study findings. The Population, Intervention, Comparator and Outcome (PICO) for each synthesis (also planned at the protocol stage) defines the question that the specific synthesis aims to answer, determining how the synthesis will be structured, specifying planned comparisons (including intervention and comparator groups, any grouping of outcome and population subgroups). The chapter focuses on the PICO for each synthesis and the PICO of the included studies, as the basis for determining which studies can be grouped for statistical synthesis and for synthesizing study characteristics. It provides a general framework for synthesis that can be applied irrespective of the methods used to synthesize results. The chapter also provides practical tips for checking data before synthesis.