Predictive MappingGMAC - Wigan 2011

Ian Bullen – Strategic Analytical Partnership Co-ordinator 9th November 2011

Wigan Strategic Assessment

“Prediction is very difficult, especially if it’s about the

future.”

Nils Bohr, Nobel laureate in Physics

Predictive Mapping

• First advanced in 2004 (Johnson et al)• Increased risk within 400m for 6/7 weeks• Local view in 2005/6 = not useful – 400m from any

Burglary in Leigh covers all of Leigh• Utilised in Trafford & linked to 25% reduction in

Burglary Dwelling• Let’s have another look…• But… “the implementation of a strategy for which

every burgled household and neighbours within 400m received crime reduction attention would require substantial resources…” (Johnson et al, 2006, Home Office)

The Changing Face of Near Repeats…

• Initial research based on 2003/4 data

• Wigan BD in 2003/4 = 2,813

• Wigan BD in 2010/1 = 1,266

• 55% reduction• Repeats and Near

Repeats also likely to have reduced

All Areas 2002

0

1

2

3

4

5

6

7

within1 week

within2

weeks

within3

weeks

within4

weeks

within5

weeks

within6

weeks

within7

weeks

within8

weeks

within9

weeks

within10

weeks

within11

weeks

within12

weeks

2002 L 1

2002 L 2

2002 L 3

2002 L 4

2002 L 5

AL L

All Areas 2010

0

1

2

3

4

5

6

7

within1 week

within2

weeks

within3

weeks

within4

weeks

within5

weeks

within6

weeks

within7

weeks

within8

weeks

within9

weeks

within10

weeks

within11

weeks

within12

weeks

2010 L 1

2010 L 2

2010 L 3

2010 L 4

2010 L 5

2010 A L L

Not Everything Repeats…

• 43% of Wigan’s Burglaries do not have a near repeat within 12 weeks

• Much more likely in Atherton and Leigh

• Ecological fallacy…

Neighbourhood Area

Burglary Offences 2010

Burglary Offences with

no Near Repeat within 12 weeks

% of Offences with no Near

Repeats

Pemberton (L1)

168 82 49%

Wigan (L2) 232 135 58%

Hindley (L3) 174 94 54%

Leigh (L4) 344 122 35%

Atherton (L5)

251 73 29%

GI* Technique

• GI* provides focus allied to statistical significance

• Some overlap with strategic clusters

• Highlights some new areas too

• But…• Are any of these

techniques predictive?

Predictive Abilities

MethodTotal Offences

Offences covered by Method

Area (sq km)

Offences per month per sq km

400m Buffers 1407 671 30.93 1.446277GI* (Previous Month) 1407 194 4.64 2.787356Strategic Clusters 1407 73 0.47 10.35461

High volumes vs manageable intervention points

More supporting analysis…

• Near Repeats identified and hotspotted• Still a large area to cover• Can we focus in any further?

‘Gaps In The Clouds’

• Near repeat hotspot• Overlaid with all 2010 Burglaries that DIDN’T see a near repeat• Reveals 4 areas where a Burglary ALWAYS sees a near repeat• Clear focus…

• Near Repeat hotspots + Analyse2Advance Clusters + GI* grids

• All 4 Near Repeat hotspots contain Analyse2Advance Clusters

• Significant grids on top of Analyse2Advance Clusters on top of Near Repeat hotspots = top priority

• Refresh GI* weekly to keep live – tactical analysis underpinned by Strategic analysis

Stacking up the Evidence

• Local picture in Leigh

Stacking up the Evidence

A Combined Approach

• Hierarchy of risk based on crimes falling into • GI* grids• Strategic clusters• Near repeat hotspots

• Identify offenders living/operating within area and target (linked to IOM work)

• Offences outside these areas should be prioritised after this but based on local knowledge of Near Repeats:– Pemberton - <300m <7days emphasis on day 1– Wigan - <300m <7 days– Hindley – no near repeat evidence– Leigh – <300m <1 day– Atherton - <200m <7 days emphasis on day 3

Current Picture

• Initial pilot exercise running since 24/10/2011• 40% strike rate – importantly, in a manageable area• Number of arrests in identified areas• Monitoring patrol locations via dip sampling• Offender element to be added in soon• Partnership approach to be developed• Works with other thematic areas – TFMV, FDR3s

Predictive MappingGMAC - Wigan 2011

Ian Bullen – Strategic Analytical Partnership Co-ordinator 9th November 2011

Wigan Strategic Assessment