Guidelines for avoiding plagiarism and self-plagiarism in PhD thesis writing

Scientific misconduct is defined¹ as fabrication, falsification, or plagiarism conducted with intent or resulting from gross negligence in the planning, execution or reporting of research. Depending on the amount of copied text and its importance for the scientific product (i.e. PhD thesis in this case), plagiarism or paraphrasing might be considered scientific misconduct by the Danish Committee on Research Misconduct.

Plagiarism
Plagiarism is the use of someone else’s text, ideas, results, methods, special terms or processes, without reference to the original source. Thus, plagiarism is more than simply using text from another source without giving due credit. Text from other sources must not be used unless it is in the form of quotation along with a reference to the original source.

Paraphrasing
Paraphrasing is reformulating or summarizing text written by another source. When this is done appropriately, the words and syntax are your own and the text is markedly different from the original, although communicating a similar content. When paraphrasing, the original source should always be referenced. Reusing sections of text where only a few words are changed or rearranged is referred to as inappropriate paraphrasing. Inappropriate paraphrasing constitutes self-plagiarism or plagiarism depending on the source.

¹According to the Danish Lov om videnskabelig uredelighed nr 383 af 26/04/2017 (in English: Act on Research Misconduct) § 3

Questionable research practice is defined as the breach of recognized standards for responsible conduct of research, including the standards put forth in the Danish Code of Conduct. Depending on the amount of copied text and its importance for the scientific product (i.e. PhD thesis in this case), self-plagiarism might be considered questionable research practice by the Practice Committee at University of Copenhagen. If the copied text originates from co-authored publications, it may even be considered plagiarism by the Danish Committee on Research Misconduct. Less severe cases of self-plagiarism in PhD theses are handled by the Graduate School at the Faculty of Health and Medical Sciences.

Self-plagiarism
Self-plagiarism is the reuse of one’s own text, figures, tables, or other content without clear indication of the reuse. This is often referred to as text recycling.
Self-plagiarism is problematic for several reasons:

• Transparency and originality: When assessing your thesis, it is important that the assessors are able to distinguish clearly between work done by you as part of your PhD studies and any work, which may have been conducted as part of previous studies or performed by others. Moreover, it is important that they can assess your contributions from co-authored publications. Therefore, the synopsis/monograph part of your thesis should be written in your own words, and you should always be transparent about the original source of quoted text, tables or figures and describe your contributions in the co-authorship declarations and the preface of the thesis when relevant.
  
  
• Co-author rights: When you share authorship of a scientific paper, you and the co-authors have collectively contributed to the contents of that paper. This means that if you reuse text, figures, or tables from that paper without disclosing the original source, you may in fact be plagiarizing content made by your co-authors which could lead to a dispute. It is important to note that such disputes may emerge at a later stage in your career, and it is therefore important to be in agreement with your co-authors from the start.
• Published papers and copyright: As a main rule the PhD thesis is not considered a publication, and PhD students are entitled to the copyright of their own unpublished manuscripts and the synopsis of the PhD thesis. But be aware that the copyright to any published articles in the PhD thesis, copied figures, tables and texts belongs to the publisher, depending on the agreement in each case.

Using your own research papers (unpublished or published) in your PhD thesis
When you write your PhD thesis, you may already have published one or more papers or written manuscripts on the work conducted during your PhD, and you may want to use this work in your thesis. The papers must appear in your thesis as chapters in the end of the thesis.

Using one or more figures from your own or others’ articles in your thesis
You may reuse your own or, with permission, others’ figures in the synopsis. There must be a clear reference to the paper where the figure originally appeared.
If you reformat the figure, the paper in which the original figure appeared should still be referenced as e.g. "Adapted from Paper X" or "Modified from Paper X".

Using text or content from previous assignments in your thesis
As a rule, the same text or content cannot be to used obtain two different academic degrees. Therefore, you cannot include text or content (e.g. results, figures or tables) from your Master’s thesis in your PhD thesis unless it is clearly marked as background information with a clear reference to the source. If results or other content from the Master’s thesis has been further elaborated during the PhD studies, the combined results/analyses can be included in the PhD thesis as long it is clearly described which parts that were conducted as part of the Master's and PhD studies, respectively.
Likewise, articles based on results from both the Master's and PhD studies can be included in the thesis as long it is clearly described which parts that were conducted as part of the Master's and PhD studies, respectively.

This is because the assessors should base their evaluation on the work that you have actually conducted during your PhD, and all work conducted before your PhD, should therefore be clearly identifiable as such.