- Make sure you understand the standards of self-plagiarism relevant to your project.
- Your institution's LMS likely provides access to an automated plagiarism checker you could use.
- Automated plagiarism checkers are imperfect.
- Some people think that commercial plagiarism checkers are unethical.
If you haven't already done so, talk to your dissertation committee about their understanding of self-plagiarism. What exactly are they concerned you might do? What are their standards, and are these standards reflective of common standards in your discipline?
Once you know how your committee understands self-plagiarism, talk to the people who administer the learning management system (LMS) at your campus. Many LMSs include access to commercial plagiarism checkers, and many of these services allow teachers or students to upload selected papers to the plagiarism checker's database. (The idea is that the plagiarism checkers allow teachers to check student work against unpublished papers that other students--like roommates or sorority sisters--have submitted in response to the same assignment in a different section of the course). If you put your publications into the plagiarism checker's database, you should be able to use the plagiarism checker to identify potential self-plagiarism.
HOWEVER, automated plagiarism checkers are imperfect. Whichever one you use, it will probably flag some stuff that isn't really plagiarism, and it might miss some stuff that is. The automated checker should supplement your own judgment, not replace it.
Finally, some people think that commercial plagiarism checkers are unethical because they collect papers and make money off of them without paying the authors. The courts have ruled that it's fair use, but you should at least know that the issue exists.