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Most likely, Turnitin is comparing the revised paper to a previous submission.

This happens because:

1. (in Canvas or Turnitin-direct) the instructor:
   

   1. did not change the Optional Settings to Generate Similarity Reports for student submissions... immediately (can overwrite until due date), and/or

   2. required the students to submit drafts to earlier Turnitin submission folder(s) and did not change the Optional Settings to Submissions to this assignment will be stored in...do not store the submitted papers.
      

2. (in Canvas or Turnitin-direct) students are required to submit reports at various stages as a group, but a different person submits each time, resulting in one submission being compared to the other.
   

3. (in Canvas or Turnitin-direct) student submits to the wrong module (class) and/or wrong assignment folder.
   

4. (in Quick Submit - staff only) the staff checked the Add file to Turnitin's repository option.

   1. Once a file is added to Turnitin's repository, the submission of a revised paper is checked against the earlier submission.

Solution

Staff can exclude the source(s) leading to the skewed Similarity Index.

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