| Effect rating | What it means |
 | Overall, evidence suggests a decrease in crime |
 | Overall, evidence suggests a decrease in crime (but some studies suggest an increase) |
 | Overall, evidence suggests no impact on crime (but some studies suggest a decrease) |
 | Overall, evidence suggests no impact on crime (but some studies suggest either an increase or a decrease) |
 | No evidence to suggest an impact on crime |
 | Overall, no evidence to suggest an impact on crime (but some studies suggest an increase) |
 | Overall, evidence suggests an increase in crime (but some studies suggest a decrease) |
 | Overall, evidence suggests an increase in crime |