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This happens because:

• (in Turnitin - direct or IVLE) the default is to finalise on first submission.
  Instructors may miss the option for not finalising Originality Report on submission as the option is located in Optional Settings.
  (in IVLE) the student submits different versions of one paper to the submission folder using different file names.
• Student ignores warning in IVLE that resubmissions should use the same file name.
Turnitin then treats the two versions as separate, comparing the recent one to the one previously submittedinstructor:

• did not change the Optional Settings to Generate Originality Reports for student submissions... immediately (can overwrite until due date), and/or
• 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.
  
  
• (in Quick Submit - staff only) the staff checked the Add file to Turnitin's repository option.
  • Once a file is added to Turnitin's repository, the submission of a revised paper is checked against the earlier submission.

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Solution

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

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Finally, please configure these settings if you have not done so:

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