Synthesis

Synthesis is the process of analyzing and interpreting evidence gathered from studies to answer a research question. While both systematic reviews and systematic maps systematically collect, screen, and organize evidence, they differ in how they synthesize information.

Systematic Reviews

Studies are synthesized using either qualitative statistical methods (e.eg. meta-analysis) or qualitative synthesis (e.g., narrative synthesis) to provide a comprehensive answer to the review question. Systematic Reviews also assess the reliability and risk of bias of each study using risk-of-bias tools, doing this helps determine confidence in the overall synthesis findings. The outcome of synthesis that has been conducted rigorously, in concert with properly executed searching, screening, selection, and extraction is detailed, decision-ready evidence that often leads to policy recommendations of best practice guidelines.

Quantitative Synthesis (Meta-Analysis)

• Combines numerical data from studies to estimate the overall effects (e.g., impacts of reforestation on carbon sequestration)
• Uses statistical methods to identify patterns, trends, and uncertainties

Qualitative Synthesis (Narrative Synthesis)

• Organizes and compares findings across studies without statistical pooling
• Useful when studies are too diverse in methods or outcomes to combine quantitatively

Systematic Maps

Study data are coded and presented in a visual format, illustrating the distribution and characteristics of the evidence base. This can involve various methods, ranging from simple spreadsheets to more sophisticated visualization or interactive databases. The outcome of synthesis is a broad overview of the evidence base and research landscape.

Study Categorization & Mapping

• Information about the studies is extracted and coded based on variables such as study location, ecosystem type, population, intervention/exposure, and study design
• Highlights research gaps and clusters of evidence in order to guide future research, funding opportunities, and areas that may have enough evidence for further synthesis

Visualizations

• Heatmaps, databases, and interactive maps illustrate what evidence exists in relation to the research question and any variables that were extracted/coded
• Provide an opportunity to see what evidence exists on the subject/topic/question and the ability to look across the evidence to examine the prevalence of specific methods, interventions, study locations, etc. to see trends across time, etc.