Scholarly journals contain more than one type of article. In one issue of a journal, for example an issue of Nature, you may find original research articles, review articles, letters to the editor, reviews of books and other materials, and more. When you are browsing articles in databases or in paper journals, keep the following questions in mind:
Original research articles are based on an experiment or study. The authors will report the purpose of the study, the research methodology, and results. This is a familiar structure for original research articles > IMRAD: introduction, methods, results, and discussion.
Review articles summarize or synthesize content from earlier published research and are useful for surveying the literature on a specific research area. Review articles can lead you to original research articles.
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Article 1: Berhe, A. A., Barnes, R. T., Six, J., & Marín-Spiotta, E. (2018). Role of soil erosion in biogeochemical cycling of essential elements: Carbon, nitrogen, and phosphorus. Annual Review of Earth and Planetary Sciences, 46, 521-548.
Article 2: Vander Linden, A., Hedrick, B. P., Kamilar, J. M., & Dumont, E. R. (2019). Atlas morphology, scaling and locomotor behaviour in primates, rodents and relatives (Mammalia: Euarchontoglires). Zoological Journal of the Linnean Society, 185(1), 283-299.
A research letter is a shorter version of a full original research article. Be aware that this is not the same as a letter to an editor in an academic journal.
Letters are often written in response to articles, editorials, and other materials. They do not go through a peer-review process, but can give you insight into the scholarly conversation around a topic. They are not included in all databases, but you may find them included in some of them.
Research Notes are short articles. They may be called short reports, technical notes, case reports etc. Be aware that some limiters in databases may also include correspondence in a Notes limiter.