A long-term assessment of the multidisciplinary degree of multidisciplinary journals

Are multidisciplinary journals truly multidisciplinary, and, how has the multidisciplinary character of these journals evolved over the long term? Here, we assess these questions by analyzing data from the Journal Citation Reports. We examined 983,246 articles and reviews published between 1980 and 2021 in 127 journals categorized under 'Multidisciplinary Sciences'. We found that the representation of the main branches of knowledge in multidisciplinary journals was uneven and, in general, not proportional to the global research effort dedicated to each branch. Similarly, the distribution of publications across specific research areas was uneven, with "Biochemistry & Molecular Biology" strongly overrepresented. However, we detected a decreasing trend in the percentage of publications that multidisciplinary journals dedicate to this and other top areas, especially over the last decade. The multidisciplinary degree of multidisciplinary journals, as measured by the Gini index, was generally low but showed a gradual increase over time. The impact factor of multidisciplinary journals was positively related to the percentage of publications in the area "Biochemistry & Molecular Biology". Compared to other multidisciplinary journals, Nature, Science, and PNAS emphasized this area even more strongly, though the difference between the first-ranked area and the other top areas consistently decreased since 1980. In conclusion, while a strong bias remains in favor of highly citable areas, multidisciplinary journals are progressively increasing their degree of multidisciplinarity in recent years. Thus, we encourage authors to carefully consider this polarization when selecting journals for their studies, and we suggest that scientific agencies keep it in mind when evaluating researchers.