Defining and Measuring Crime
What Counts as a Crime?
Every day, newspapers report on offences ranging from shoplifting to murder. But what actually makes an act a crime? Psychologists studying criminal behaviour need a clear picture of what counts as criminal, because this shapes how researchers study it and how governments respond to it. The specification groups criminal behaviour into five types: violent, drug-related, acquisitive, sexual and anti-social offences.
Psychologists classify crime into five types: violent, drug-related, acquisitive, sexual and anti-social offences. Each type involves a different kind of harm and can be measured differently.
The Five Types of Crime
Violent crime involves physical harm or the threat of harm to another person, such as assault or robbery involving force. Drug-related crime covers the production, supply or possession of controlled substances. Acquisitive crime is committed for financial or material gain — theft, burglary and robbery are common examples.
Sexual offences involve non-consensual sexual acts, and anti-social offences cover criminal behaviour that causes, or is likely to cause, harassment, alarm or distress to people who are not of the same household as the offender — for example, vandalism, graffiti or persistent noise nuisance from a neighbour. These categories often overlap in practice: a robbery involves both violence and acquisitive gain, and a burglary carried out under the influence of drugs touches on three categories at once.
Categorising crime helps psychologists compare like with like when they study causes and treatments. A theory that explains violent crime, such as a build-up of frustration, may not explain drug-related crime, which is often linked to addiction or financial pressure. Governments also use these categories to decide how to allocate police resources and to design targeted crime-prevention campaigns.
Crime as a Social Construct
Psychologists argue that criminal behaviour is a social construct. This means an act is only criminal because a particular society, at a particular time, has decided to make it illegal. It reflects deviation from norms — norms being the unwritten rules a society expects people to follow. For example, behaviour that was once criminalised in Britain has since been decriminalised as social attitudes shifted, showing that the law follows social norms rather than any fixed moral truth.
Culture plays a central role in defining what is criminal. Laws around alcohol, drugs, gambling and even certain forms of protest differ hugely between countries, showing that crime is not a fixed, universal category but one shaped by cultural values and social attitudes. Behaviour that is a serious criminal offence in one culture may be legal, or even encouraged, in another.
Crime is a social construct: an act is criminal because a society has agreed to define it as deviation from its norms, not because the act is inherently wrong in every culture and every era.
How Psychologists Measure Crime
Official statistics are figures collected by the police and government bodies from crimes that have been reported and recorded. They are useful because they cover very large numbers of people and allow comparisons across regions and over time. However, they only capture crimes that victims chose to report and that police chose to record, so they miss a large amount of unreported offending, sometimes called the “dark figure” of crime. Recording practices also change over time — if police forces start recording a type of incident they previously ignored, official statistics can show a rise in crime even though real offending levels have stayed the same.
A self-report study asks people directly about crimes they have committed, often through anonymous questionnaires. This method can reveal offences that never reached the police, including minor drug use or anti-social behaviour. For example, a self-report survey might ask teenagers anonymously whether they have ever taken an illegal drug, revealing behaviour that would rarely appear in police records. Its main weakness is that respondents may lie, exaggerate or forget, especially about socially disapproved behaviour, which affects the accuracy of the data.
Official statistics give a reliable, large-scale picture of crimes that reach the criminal justice system, but under-represent unreported offences such as domestic violence or minor drug use. Self-report studies capture more of this hidden crime, but rely on the honesty of participants and cannot be checked against an independent record. Psychologists often use both methods together to build a fuller picture of how much crime actually occurs.
Understanding how crime is defined and measured gives psychologists a foundation for studying why people offend — the theories and applications covered later in this topic, such as Social Learning Theory and Eysenck’s Criminal Personality Theory, build directly on this idea that criminal behaviour is socially defined and imperfectly recorded.