In the similarity report of turnitin, the similarity index, internet sources, publications and student papers percetages are given. What is the relation between similarity report and the remaining?.

Does the internet source, publications and student papers adds to get similarity index?

In the attached case, similarity index is 14%, internet sources is 11%, Publications is 12%, student papers is 0%.

Then 11% + 12% + 0% is not equal to 14% naa. So How to relate them.