Research Article
An article reporting on the results of one or more studies or experiments, written by the person(s) who conducted the research. This is considered one type of primary source. Look in the title or abstract for words like study, research, measure, subjects, data, effects, survey, or statistical which might indicate empirical research.
Example: Zehnder, C., & Hunter, M. (2008, February). Effects of nitrogen deposition on the interaction between an aphid and its host plant. Ecological Entomology, 33(1), 24-30.
Review Article
An article summarizing the results of significant studies or experiments, often attempting to identify trends or draw broader conclusions. Although scholarly, it is not considered a primary source or research article, but its references to other articles will include primary sources or research articles.
Example: Parker, M., & Thorslund, M. (2007, April). Health trends in the elderly population: Getting better and getting worse. Gerontologist, 47(2), 150-158.
Theoretical Article
An article containing or referring to a set of new or established abstract principles related to a specific field of knowledge; characteristically it does not contain original empirical research or present experimental data, although it is scholarly.
Example: Gestrich, A. (2006, August). The public sphere and the Habermas debate. German History, 24(3), 413-430.