Trends in the Systematic Literature Reviews Over the Years

OBJECTIVES: Nowadays, systematic literature reviews (SLRs) and meta-analyses are often placed at the top of the study hierarchy of evidence. The main objective of this paper was to evaluate the trends in SLRs of randomized controlled trials (RCTs) throughout the years.

METHODS: Medline database was searched via the Ovid platform, using a highly focused search strategy. A single screening of titles and abstracts was performed. Based on the information provided in titles and abstracts, each included paper was coded according to a specific ICD-10 chapter (depending on the disease area or procedure). The number of RCTs included in each evaluated SLR was also retrieved. All SLRs analyzing RCTs were included, without any restrictions on population, interventions, or outcomes. Protocols, commentaries, or errata were excluded. No other restrictions were applied.

RESULTS: After deduplication, 7,465 titles and abstracts were analyzed, from which 6,892 were included for further analyses. The oldest retrieved publications date back to 1994. There was a gradual increase in the number of annual published SLRs, and a significant increase in published articles during the last several years: from over 800 publications in 2020 to over 1,400 papers published in 2022. Overall, the most frequently analyzed area were diseases of the circulatory system (n=750), closely followed by endocrine, nutritional, and metabolic diseases (n=734). Interestingly, this trend is reversed in the latest years –in 2019 and later, endocrine diseases were more frequently evaluated (n=394). The majority of SLRs included between 11 and 50 RCTs each.

CONCLUSIONS: The recognition of SLRs’ usefulness is growing at an increasing speed. The rapid increase in the number of published SLRs in the last 3 years was only partially caused by the emergence of COVID-19. The most frequently evaluated diseases are in alignment with leading causes of death and disability worldwide indicated by the World Health Organization.