Please let us know any studies that compare features of concept mapping with outlining. Many studies have reported both outlining and concept mapping helpful for learning and assessment, but they looked at them as black-boxes. On one hand, although outlining has been around for longer, there are significantly more studies that indicate the effectiveness of concept mapping for learning and assessment. On the other hand, outlining is more widely used among students and researchers. Then, what are the features that differentiate them? Are there specific features that are helpful for some applications but not others?
Here is what we already know: Miyatsu et al.  define the following procedure for outlining:
- Read the entirety of the original passage.
- Keep in mind how the author structures ideas.
- Identify main ideas.
- Structure main ideas in the outline.
- Use outline as a cue to retrieve information.
These steps are very similar to the procedure advised by Novak and Cañas [2, 3] about designing a good concept map. Especially, steps three and four in the outlining procedure correspond to the progressive differentiation and integrative reconciliation processes defined in Ausubel's Assimilation theory , which are the foundation of the concept mapping. Mayer  found outlines as "advance organizers" helpful to facilitate "bridging," i.e., the thinking process one goes through to connect the new knowledge with what they already know . This thinking process results in meaningful learning that is shown to be improved through concept mapping . Lehman et al.  compared outlining with concept mapping, but found no significant differences between their uses, although results were leaning towards greater improvements with the mapping condition. Also, Bui and McDaniel  compared the use of skeletal outlines to illustrative diagrams in improving free recall and short-answer questions; while both conditions were significantly effective for free recall compared to a control, those using illustrative diagrams had performed significantly better than students using skeletal outlines, particularly for low-ability learners. Therefore, free recall may not depend on how students organize or visualize information, but it does effectively change improvements in short answer questions. Kiewra  compared using matrices against outlining on comparative information, with the former having visual properties that allow users to create relationships between different categories of information that the latter often overlooks. Hansell  suggested the use of "post organizers" or "arrays," which use a combination of "words, lines, and arrows," similar to that of concept maps. This was shown to have significantly improved the ability for students to outline as it focuses on "identifying relevant ideas and fitting these into a meaningful pattern." As a result, the visualization of information may have played a large role in enabling students to process information to a deeper level.
1- Miyatsu, T., Nguyen, K., & McDaniel, M. A. (2018). Five popular study strategies: their pitfalls and optimal implementations. Perspectives on Psychological Science, 13(3), 390-407.
2- Novak, J. D., & Cañas, A. J. (2008). The theory underlying concept maps and how to construct and use them. Florida Institute for Human and Machine Cognition, 2008.
3- Cañas, A. J., Novak, J. D., & Reiska, P. (2015). How good is my concept map? Am I a good Cmapper?. Knowledge Management & E-Learning: An International Journal, 7(1), 6-19.
4- Ausubel, D. G. (1963). Cognitive Structure and the Facilitation of Meaningful Verbal Learning1. Journal of teacher education, 14(2), 217-222.
5- Mayer, R. E. (2008). Applying the science of learning: Evidence-based principles for the design of multimedia instruction. American psychologist, 63(8), 760.
6- Lehman, J. D., Carter, C., & Kahle, J. B. (1985). Concept mapping, vee mapping, and achievement: Results of a field study with black high school students. Journal of Research in Science Teaching, 22(7), 663-673.
7- Bui, D. C., & McDaniel, M. A. (2015). Enhancing learning during lecture note- taking using outlines and illustrative diagrams. Journal of Applied Research in Memory and Cognition, 4(2), 129-135.
8- Kiewra, K. A. (2002). How classroom teachers can help students learn and teach them how to learn. Theory into practice, 41(2), 71-80.
9- Hansell, T. S. (1978). Stepping up to outlining. Journal of Reading, 22(3), 248-252.