Reuse of your own work

The reuse of your own work without citing the source can lead to several negative consequences, albeit on a smaller scale than is the case with plagiarism: 

  1. In the case of substantial and frequent reuse: disruption of the rightful assignment of credit (too much credit to the author).
  2. Misleading the public, editor and/or publisher regarding the originality of the work. The scope of this possible effect is reasonably restricted by the consideration that the legitimate expectations of the public and publisher regarding originality should always be limited. Because science is incremental, no publication is ever completely new or innovative, and all publications, at least in part, build upon previous work by others and, in many cases, the author in question. 

In the case of small-scale reuse of your own material without citation (e.g. a few sentences or a paragraph), the above-mentioned negative effects are negligible or non-existent. This means that the small-scale re-use of original texts without citation is usually not problematic, particularly with regard to the re-use of short passages, texts and ideas in the introduction, theoretical development and method description. In such cases, converting such a self-repetition into a cited quotation will often produce a stilted or inelegant result. More extensive cases of the re-use of original texts without citation can reach a level that may not be elegant, but does not quite fall into the category of Questionable Research Practices either (QRP). The re-use of original texts or ideas without citation on a scale at which the above-mentioned effects could occur does constitute QRP. This also applies to the re-use of empirical research results without citing the source. This is more problematic than the re-use of texts or ideas in the introduction, theoretical development or method description. This is not only because the innovative character of scientific publications usually lies in the research results – an aspect to which editors and publishers take a highly critical approach – but also because it can lead to a distortion of the research results. Although these considerations do add some significant nuances to a grey area, they do not establish any boundaries that are absolute and applicable in all circumstances. Once again, in the framework described above such cases must ultimately be weighed up by peers who are sufficiently familiar with the scientific field

Source: Koninklijke Akademie van Wetenschappen (Royal Academy of Arts and Sciences), advisory brief, correct citation.