Understanding & Interpreting the similarity index

Simillarity PercentageThe similarity index is the composite number returned after the text matching has taken place. Displayed as a percentage, the number ‘is a measure of the percentage of the paper that the system was able to find matching text for, regardless of whether or not the text was properly cited.’

Similarity Red/Amber/Green

A traffic light visual checking system is used to display low, medium, and high matches for a quick visual scan across the results.

For a full interpretation of the “score”, staff are reminded to reveal the composite matches, which make up the overall score. Typically a similarity index can comprise of many 1, 2, 3% insignificant matches – with additional higher matches.


It is possible to filter out or exclude the “noise” of the less significant (smaller) matches to concentrate on the higher (more significant) numbers. But again, each case is unique, so a suspect script may need closer inspection if other factors have a bearing on the results.

How to interpret your Turnitin report

Oxford Brookes University

Lindsay Williams, Senior Lecturer in Business and Management at Oxford Brookes University , discusses how to interpret a Turnitin report using real examples. The composite number which is known as the similarity index is discussed in detail, covering related issues such as false positives.  It must be noted that this video is aimed at students. You can also view the material on Oxford Brookes’ repository.

Note At Aston University we have a policy of not allowing students access to the Turnitin orginality report.