70% of late assignment excuses are lies

Joseph Ferrari, a psychology professor at DePaul University and editor of Counseling the Procrastinator in Academic Settings, found in one study that "students who engaged in academic procrastination said more than 70 percent of the excuses they gave instructors for not completing an assignment were fraudulent (the lies were most prevalent in large lecture classes taught by women who were "lenient")."

Quoted from:
Hoover, Eric. (2005). Chronicle of Higher Education, 52(16), A30-A32.