Most of the data are taken from information recorded or reported by the police.
Comparisons of crime levels based on the absolute figures would be misleading, since they are affected by many factors including:
- different legal and criminal justice systems
- rates at which crimes are reported to the police and recorded by them
- differences in the point at which crime is measured (for example, report to the police, identification of suspect, etc.)
- differences in the rules by which multiple offences are counted
- differences in the list of offences that are included in the overall crime figures.
As a general rule, comparisons should be based upon trends rather than upon levels, on the assumption that the characteristics of the recording system within a country remain fairly constant over time. Where national series without definitional changes are available, general trends have been estimated. Please consult the Methodological Notes for further information.