Systematic Reviews & Evidence Syntheses

Secondary research gathers and analyzes data focused on or around a specific question. Often this is a question that has been asked by several different researchers at different points in time, yet no clear consensus has been reached in the literature. Alternatively, this could be an investigation into the underlying methodologies, sources, definitions or assumptions in published work. Some examples:

• How has political expression been defined and measured on social media? (Lane et al., 2022)
• Have technological innovations in photovoltaic electricity impacted that industry's environmental sustainability? (Blanco et al., 2020)
• What are the effects of sediment exposure on coral reef systems? (Tuttle & Donahue, 2022)
• What are the characteristics of gene expression datasets used in machine learning work? (Grisci et al., 2023)
• What have been the experiences of health practitioners and consumers who work together for better planning, evaluation, and understanding of health services? (Merner et al., 2023)

Systematic reviews, meta-analyses, evidence syntheses, and other types of reviews are all referred to as secondary research. As shown in the image above, they are at the top of the hierarchy of evidence.