Publication rates for systematic reviews (SRs) have grown, while the rate of publication of original research may not be keeping pace. It is unclear whether these trends are sustainable and are reflected in imaging research.
To evaluate the epidemiological characteristics, publication rates and sustainability of SRs in imaging journals.
A MEDLINE search identified SRs published in 72 imaging journals from 1 January 2000 to 31 December 2016. We screened the articles retrieved against the inclusion criteria. We extracted demographic and methodological characteristics from eligible studies. We evaluated temporal trends using linear regression and Pearson correlation coefficients (r). We calculated the 'sustainability coefficient' based on a ratio of all published non-SRs to the primary studies included in all SRs; a value > 1 suggests sufficient primary study publication to sustain SR output.
We included 921 SRs, which reported on 27,435 primary studies, 85,276,484 patients and which were cited 26,961 times. From 2000 to 2016, the SR publication rate increased 23-fold (r = 0.92, P < 0.001) and the proportion of SRs to non-SRs increased 13-fold (r = 0.94, P < 0.001). SR publication rates for the top five countries are shown by year (Figures 1) and journal impact factor (Figure 2). Table 1 illustrates temporal trends for types of SR, meta-analyses, author teams and funding. Diagnostic test accuracy SRs were most frequent (46.5%) of which one in five compared more than one diagnostic test. Most SRs did not report funding status (54.2%). The reporting of funding and the proportion of non-funded SRs increased over time. The median author team size was five; this increased over time. An imaging specialist co-author was included in 67.3% of studies; this decreased over time. Most SRs included a meta-analysis (69.6%) and a minority included an individual patient data meta-analysis (11.1%). Journal impact factor positively correlated with SR publication rates (r = 0.54, P < 0.001). There were 168,074 non-SRs published with a sustainability coefficient of 6.13.
The SR publication rate is increasing rapidly compared with the rate of non-SRs. However, the present sustainability coefficient appears to be supportable; monitoring of the sustainability coefficient may be warranted to ensure SRs remain sustainable in imaging journals. Epidemiological SR features changed over time.