Politicians and other students caught in plagiarism?

It is a controversial question (especially, if it refers to politicians). The issue of academic misconduct is an everlasting problem. A lot of famous people and thought leaders (including Martin Luther King) plagiarised and used other people’s ideas in their papers. Previously it was:

1. hard to detect plagiarism, as there were no such innovative technologies and software;
2. the requirements were not so strict towards the authenticity of the papers. With the lapse of time plagiarism detection software was developed. Nowadays, no software can detect any type of cheating and has access to all the repositories available. It is just impossible as there is no common international repository for all academic institutions. Each university has its database and access to it is not granted to any third-parties. The leading academic plagiarism checkers like Turnitin, Unicheck, have access to many private databases, improve their algorithms all the time and deploy new innovative products (authorship verification by Unicheck, or iThenticate by Turnitin). Still, the cheating methods are also ‘improved’ and changed every day. To combat academic dishonesty on time, the mixture of actions has to be applied where plagiarism software is only one of them.

Actually, it is not just politicians. The media only report on politicians, though. I work with the VroniPlag Wiki academic group, there are over 200 published documentations of plagiarism, and many of these degrees have been revoked: http://de.vroniplag.wikia.com/wiki/%C3%9Cbersicht (sorry, in German, but you get the gist).

As others have noted, Turnitin and other systems are just a tool, not a litmus test for plagiarism. They can only find what their algorithms can find in the database they have been able to populate. There are very many false positives and even more false negatives. The reports are very difficult to interpret, to boot.

For your particular question, I know from my work testing plagiarism detection systems that very many repositories of dissertations are not indexed by the software. One reason is that they are very difficult to traverse (and each has a different structure). There only tend to be the dissertations stored in the databases that have previously been checked. So in your case, if the student's thesis A was not checked, it was not in the database when B was potentially checked. But if a human reader sees that the topic is the same and then compare's thesis A with thesis B, they can quickly see and document the overlap. And of course, not all theses are checked, for various reasons, not all of which are academic in nature.

If you want to know more about the work that goes into documenting plagiarism in (oldish) theses, I blogged about that ages ago: https://copy-shake-paste.blogspot.com/2012/10/how-to-find-plagiarism-in-dissertations.html (in English).

Turnitin is not a fire and forget tool, it requires significant human effort to go through the results and separate serious plagiarism from sloppiness from outright false positives. Doing it retroactively is even harder because you have to carefully check who copied who.

Also turnitin only looks for straight text copying, it doesn't look for the (IMO more serious) stealing of ideas.

And of course it's not omnipresent either, lots of stuff (even stuff that is online) isn't in their database.

For normal students noone cares enough to do the work of trudging through old thesis looking for plagarism, famous politicians and other people who lots of people have a grudge against are another matter.

Turnitin and other tools are mainly (exclusively) Internet based plagiarism tools. They check if a submitted piece of work contains passages that match those found elsewhere on the Internet or previously submitted to the tool.

There are many sources that are not on the internet and created before such tools and technology existed. Any plagiarism from those would not be detected by things like TurnitIn.

In particular the historical (i.e. before 21st century) thesis archives of most university libraries have not yet been digitised and made Internet browsable. If someone just copied one and handed it in as theirs, then the only protection from plagiarism is the knowledge and experience of the examination panel (who would be expected to be familiar with prior works).

A further reason might be that not all institutions require the submission of a thesis in machine readable form. You can only use Turnitin on document files like word or PDF. You cannot (easily) use such tools for physical paper copies of a thesis. Some universities might still take submission as a bound book making detection mechanically difficult. Further, they might just not subscribe to TurnItIn et.al. as they might be too expensive and rely on the old human element instead.

This is why, when such blatant copying is later discovered a degree might be revoked.