This post was edited on 01 Feb 2013 to add an additional point
I was interested to see the stats which Turnitin have released showing the sources which students’ work is most frequently matched against. In particular, they highlight that Wikipedia is a source which students’ work is frequently matched against. But is it really that clear cut?
The full paper, which is available on request, doesn’t say much about the methodology of the research, which leaves several questions unanswered.
One potential methodological criticism of this study is that it relies on Turnitin matches. More able students are likely to be paraphrasing the sources they have consulted rather than quoting verbatim – although this practice varies between disciplines – and such paraphrasing would not show up in a Turnitin originality report. Arguably, therefore, this study only reflects the sources that weaker students are using in their work.
A further criticism is that the paper does not make it clear whether they are looking at just the match which is initially shown when you open the originality report or every match that it finds.
Consider this example from an originality report, where the highlighted source is Wikipedia. Drilling down into the Match Breakdown section, you see that there are four other sources that have an equal match of 5%. Clicking them in turn highlights the exact same phrases in the student’s paper as were matched with Wikipedia.
So it seems that Turnitin may have a bias towards Wikipedia, listing it first amongst potential sources where there are multiple identical matches for the same content. (This is perhaps because of the nature of a wiki and the redirections on the site that mean each page has several URLs so it is listed multiple times, as in this example.)
Given that anybody can edit Wikipedia, it is perfectly plausible that the Wikipedia article has quoted (or plagiarised) the same source that student has used. It is also possible that students are citing Wikipedia content without knowing it, where it has been reused on other sites which might look more credible (which Wikipedia encourage by publishing under a Creative Commons license).
So while Turnitin’s advice in the full paper that students be guided to follow the links from Wikipedia to the original source is perfectly sound, there is every chance that it could still show up as a match against Wikipedia in the originality report, and thus in any future updates to these statistics.