In a 2017 meta-analysis of five studies, 3.5% of a total of 1,378 students reported having bought assignments to submit as their own. Of the students who reported engaging in contract cheating, more than 60% admitted to having done so more than once.[14] A larger systematic review of 65 studies from 1978 to 2016 also found that 3.5% of students admitted to engaging in commercial contract cheating.[15] Subsequently, a study of over 14,000 Australian students found that 5.8% of students engaged in one of five behaviours classified as contract cheating, with 2.2% submitting assessments completed by other people.[3] However, a 2021 study argued that anonymous self-report surveys underestimate the extent of contract cheating, and using an incentivized truth-telling methods, it suggested that 7.9% of students buy and submit custom-written assignments while 11.4% submit assignments downloaded from file-sharing sites as their own.[16]