Dark figure of crime

The dark (or hidden) figure of crime is a term employed by criminologists and sociologists to describe the amount of unreported or undiscovered crime.
Methodology.
This gap between reported and unreported crimes calls the reliability of official crime statistics into question, but all measures of crime have a dark figure to some degree. The gap in official statistics is largest for less serious crimes.
Comparisons between official statistics, such as the Uniform Crime Reports and the National Incident-Based Reporting System, and victim studies, such as the National Crime Victimization Survey (NCVS), attempt to provide an insight into the amount of unreported crime.
Self-report studies are also used in comparison with official statistics to assess the dark figure of crime.