testing the effectiveness of geo- behavioural profiling systems professor david canter & laura...
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Testing the Effectiveness of Geo-
Behavioural Profiling Systems
Professor David Canter
&
Laura HammondDirector, Centre for Investigative Psychology
The University of Liverpool,UK
www.i-psy.com
Study of effectiveness of various prioritisation
strategies
92 offence series
in a London borough.
All identified series
over four years/
Various Models Illustrated from the crimes of Jack the
Ripper
The ‘canonical’ map
Nichols 31.8 –3.40Chapman 8.9 – 6.00
Stride 30.9 – 1.00Eddowes 30.9 – 1.45
Kelly 9.11- 7.00?
The ‘canonical’ map
Circle Hypothesis Calculation to Locate Ripper’s Base
Central Circle in Whitechapel
Centre of Gravity of Murder Locations
Two further concepts
Criminal Range Decay Functions
Criminal ‘range’
0-0.10.11-0.5
0.51-0.991.00-1.5
1.51-2.002.01-2.5
2.51-33.01-4
4.01-55.01-6
6.01-77.01-8
10+
0
5
10
15
20
25
30
35
Range of Distances traveled by Arsonists
The Distance Decay Function,An example from serial arsonists
Optimal Function of Distance from Offence to ‘Home’
Offence Map:
Developing the Search Tool that incorporates various distance functions.
1st Crime2nd
3rd
4th
5th
The system assigns a priority to each known offender using
various criteria.
Offender ID Address ProbabilityMO Match
124 Location A 0.28574311864 0
427 Location B 0.27038233898 0
427 Location C 0.26035169492 0
226 Location D 0.25577861017 0
48 Location E 0.23282991525 0
124 Location F 0.22445984746 0.3
124 Location G 0.21932662712 0
Prioritised search area
50% of actual offenders are in the top 5 prioritized just by geographical location. iOPS allows this to be improved by also using M.O. matching.
Criteria
• Distance from centre of circle defined by 2 furthest crimes
• Distance from centre of gravity (centroid)
• Optimum negative log decay function
• Negative log decay function with buffer
(N = 92)
Model Mean Rank (S.D) Median Rank
Exponential Function - High B-value 8.86 (8.446) 4
Logarithmic Function -Low B-value 9.04 (8.402) 4.5
Logarithmic Function -High B-value 8.92 (8.350) 5
Centre of Gravity 9.21 (8.256) 5
Logarithmic Function -Optimal B-value 8.95 (8.349) 5
Logarithmic Function with Buffer Zone- Optimal B-value 9.73 (8.674) 5.5
Exponential Function - Low B-value 10.18 (8.411) 7
Exponential Function - Optimal B-value 10.55 (8.461) 7
Exponential Function with Buffer Zone- Optimal B-value 10.61 (8.888) 7
Last Offence 11.11 (8.416) 9
First Offence 11.96 (8.424) 10..5
Centre of Minimum Distance 12.52 (8.066) 14
Centre of Circle 15.15 (7.536) 21
Straight Linear Function 21.00 ( .000) 21
COMPARISON OF 15 DIFFERENT MODELS
Need for more context specific examination of crime patterns
Taking account of Land use Opportunities for crime Guardianship Targeting Transport routes Temporal sequences
Offender 1:
34 CRIMES
1 HOME LOCATION
Offender
34 crimes
1 home location
Offender 2:
34 CRIMES
1 HOME LOCATION
Offender 34 crimes1 home location
2 Offenders with different distributions of crimse in relation to Southside Centre in Wandsworth
Southside Centre
Offender
34 crimes
1 home location
Offender 34 crimes1 home location
EXAMPLES FROM BURLGARIES IN WANDSWORTHPNC data
12 offenders
All crime types
1992-present
Offender 1:
10 CRIMES
2 HOME LOCATIONS
Offender 8:
24 CRIMES
1 HOME LOCATION
Offender 3:
20 CRIMES
3 HOME LOCATIONS
Offender 2:
21 CRIMES
3 HOME LOCATIONS
Offender 7:
13 CRIMES
2 HOME LOCATIONS
Offender 5:
19 CRIMES
3 HOME LOCATIONS
Offender 11:
48 CRIMES
3 HOME LOCATIONS
Offender 12:
53 CRIMES
2 HOME LOCATIONS