A recent paper looks at the geography of plagiarism. Paper is here. They looked at preprints on the arXiv and used sophisticated algorithms to look for text reuse that was not attributed. Not too surprisingly, certain countries have much higher reuse rates. China is one of the high rates, but it is interesting to note that Bulgaria and Egypt had higher rates- but that may be due to small sample sizes in those countries. An article about their work can be found here.