How do we analyse crime statistics?

Lucy Snowball

NSW Bureau of Crime Statistics and Research

About me

• Bachelor of Arts/Commerce

– Statistics, maths and economics

• Statistician at the Bureau of Crime Statistics and

Research

– Use statistical methods to analyse crime and offending

patterns

About BOCSAR

• Data from police and court records

• Types of research– Who gets sentenced to prison?

– Juvenile offending

– Social and economic factors that affect involvement in crime

– Predict re-offending

Methods we use

• Summary statistics – Mean, standard deviation, median, mode, range

• Time series analysis– Increasing/decreasing trends

– Break points

• Regression modelling– Building an equation to see which factors influence

others

Factors to consider

• How is the offence recorded?• Which groups are most likely to commit

this offence (young people, men, people in cities)

• What effect will policing policies have?• What external factors might affect rates

– The economy, government policies, commercial decisions, other crime rates

Example: Narcotics use• Heroin is the most common narcotic• Police record each time they arrest a person for use or

possession of a narcotic• Offenders: young people (18-30), people in major cities

(Sydney, Newcastle, Wollongong)• The time series can reflect actual use or policing

strategies• All drug use is affected by the availability of that drug• Effects other crimes - Narcotics linked to property crime