The University of Canterbury had just 17 cases - suggesting differences in what institutions consider cheating, and how they target and record it.
Asked about its high numbers, a University of Waikato spokeswoman said all complaints were dealt with through a single discipline committee, "ensuring one central process and therefore robust record-keeping".
A spokesman from the University of Canterbury said its low number of cases reflected vigilance by staff and tough penalties including fines.
Universities have been put on notice about academic dishonesty since reports exposed companies apparently using "ghost writers" to complete assignments for paying students.
A High Court judgment last month froze assets of an Auckland couple linked to one such company, and the New Zealand Qualifications Authority has produced advice on how to stop the practice.
Figures released to the Weekend Herald show there were four confirmed cases of students purchasing assignments at Massey University last year.
A Massey spokesman said:"The lecturer looked at the electronic files, spoke to the students and established they had all commissioned a particular business to complete individual assessment problems for them.
"The business provides services for customers via the internet. The business is a legitimate business and not set up to provide assignments to order, or make profits by enabling students to cheat."
Massey did not believe students purchasing assignments was a significant problem, he said.
"It is treated seriously and in this case the students were found to have committed a level three breach of academic integrity [the most serious level] and could have been excluded but chose to withdraw once that was put to them."
AUT said it identified two instances last year where students had bought assignments. Auckland, Waikato, Canterbury, Lincoln and Victoria Universities all said they had no such cases.
Plagiarism - using others' work without attribution - accounted for most misconduct cases.
One University of Auckland student was fined $600 and received no mark after helping a friend complete a written test by swapping test papers, and a PhD student was expelled after their thesis proposal was found to be plagiarised.
Another student made up references, and a University of Otago student received a warning after their assignment mirrored another's.
Universities use content-matching software such as Turnitin. While these can help identify plagiarism from public sources, they cannot flag plagiarism from other students or cheating such as purchasing "ghostwritten" assignments.
According to NZQA, signs of ghostwriting can include breadth of research, writing style, use of terms not specifically related to the topic, spelling or terminology not usually used in New Zealand, and referencing or essay construction the student has not previously used.
Other students should be encouraged to act as "whistleblowers", NZQA advises.
Emails to senior managers can provide a confidential channel for student complaints about suspected dishonesty.
