Solvability Analysis:Increasing the Likelihood of detection in Completed,

Attempted and In-Progress Burglaries

Colin Paine & Barak Ariel

• All residential burglaries in Thames Valley from 1st March 2010 to 31st October 2011

•11,769 full offence residential burglaries

•Excludes distraction burglary, aggravated burglary and non-residential burglaries.

Data Set I

• All residential burglaries in Thames Valley from 1st March 2010 to 31st October 2011

•2,537 attempted residential burglaries

•Excludes distraction burglary, aggravated burglary and non-residential burglaries.

Data Set II

• All in-progress residential burglaries in Thames Valley from1st November 2009 and 31st October 2012 (i.e. Burglary emergencies).

•N = 6,119

•Includes aggravated, distraction and non residential burglaries.

Data Set III

Collapsed four databases:• “Socrates” – the forensic information database• CEDAR – the crime recording database• IMM – the crime investigation management application• Command and control – the incident resourcing

system (only this system used for data on in-progress offences).

• (Datasets aligned using crime numbers & cleansed to remove duplicates)

Data Sources

LimitationsUnable to study ‘Suspect Named’ variable (Greenberg 1970).

Unable to study intelligence as a variable

Insufficient capacity to study ANPR as a variable

Full and Attempted Burglaries

129 variables in the data set 57 useful variables, such as:

1. Time range of offence, 2. time to first officer attendance, 3. offence witnessed, 4. suspect seen, 5. suspect disturbed, 6. fingerprints recovered, 7. DNA recovered, 8. items left at scene by offender, 9. rural/town location, 10. media appeal completed, 11. called in as burglary in progress.

Variables

Non-Dwelling Burglary

Dwelling Burglary

Distraction Burglary

Aggravated Burglary

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

2000018029

14306

362 61

Burglary Offences by Catagory

43.7% of all burglaries are residential (dwellings)

0

4000

8000

1200011769

2537

Number of Burglary Dwelling Of-fences (Completed Offences and

Attempts)

17.7% of Residential Burglaries are Attempts.

00:00 - 1...

01:00 - 0...

02:00 - 0...

03:00 - 0...

04:00 - 0...

05:00 - 0...

06:00 - 0...

07:00 - 0...

08:00 - 0...

09:00 - 0...

10:00 - 1...

11:00 - 1...

12:00 - 1...

13:00 - 1...

14:00 - 1...

15:00 - 1...

16:00 - 1...

17:00 - 1...

18:00 - 1...

19:00 - 1...

20:00 - 2...

21:00 - 2...

22:00 - 2...

23:00 - 2...

0100200300400500600700800900

Frequency of Burglary Offences by Time of Day

Most burglaries do not occur at night

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

Sunday

0500

10001500200025003000

Frequency of Burglary Of-fences by Day of week

Description of Dataset(Solved Residential Burglary)

0

200

400

600

800

1000

1200

1400

1600

1344

522

32 20 5 2 1

Burglary Detection by Type

69.8% of detections are charges.

Solved Crimes• Detected crime selected as

the definition of solved crime. 1926 detected crimes (12.99%)

• Removed secondary detections – 525 removed

• 1401 detected crimes (9.79%)

• 4 methods of disposal included; charges, reprimands, final warnings, cautions.

• Majority are chargesBurgl

aries C

harg

ed

Juve

nille R

eprim

and

Juve

nille fin

al warn

ing

Adult C

autio

n0

200400600800

1000120014001600

1344

5 20 34

Number of Disposals For Residential Burglary 01/03/10 to 31/10/11

Attempted burglary

Full burglary Total0.00%

5.00%

10.00%

15.00%

5.68%

10.68% 9.79%

Detection rates of Residential Burglaries 01/03/10 to 31/10/11

Attempted burglary is harder to solve than the full offence.

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 1900

10

20

30

40

50

60

70

Number of days to detect Burglary (exclud-ing 10% and 90% Percentile)

No. of days to detect

No.

of b

urgl

arie

s

Mean 41 daysMedian 25 daysMode 3 days

Over 96% of all detections are obtained in 180 days. 1 Burglary took 5 and half years to solve.

Solvability Analysis

Data Quality Assurance and Cleansing

•Random selection and review of quality of data capture in 100 burglaries from the sample

•Review of missing data to determine whether it will undermine internal validity.

•Data was pretty good!

0.00%2.00%4.00%6.00% 4.93%

1.39%0.27% 0.12%

Percent of cases where a footwear mark is recovered

Detected cases %Undetected Cases %

Compared percentage of marks recovered in solved sample and unsolved sample.

0.00%4.00%8.00%

12.00%13.29%

9.72%

0.90% 1.00%

Percent of cases where DNA is recovered

Detected cases %Undetected Cases %

Compared percentage of marks recovered in solved sample and unsolved sample.

0.00%

10.00%

20.00%21.24%

13.89%

3.61%1.00%

Percent of cases where a fingerprint is recovered

Detected cases %Undetected Cases %

Compared percentage of marks recovered in solved sample and unsolved sample.

0

10

2030

22.19

30.55

9.16 9.9

Percent of cases with one or more witnesses recorded

Detected cases %Undetected Cases %

Burglary in progress (full burglaries)

Burglary in progress (attempt burglaries)

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

8.43%

19.44%

3.86%

5.97%

Percent of cases initially reported as a burglary in progress

Detected cases %Undetected Cases %

Compared percentage of burglaries in progress in solved sample and unsolved sample.

0

100

200

300

144.94116.22

178.17

260.51

Average (mean) time to attend-ance of first officer (minutes) excluding burglaries in pro-

gress

Detected CasesUndetected Cases

New solvability factors identified: media appeal, vehicle stolen in the crime, anything left at scene by the offender, stolen property recovered, reported as a burglary in progress, DNA and footwear marks recovered.

The most powerful solvability factors occur the least often.

Premise

s were

occu

pied

Any st

olen p

ropert

y rec

overe

d

Offend

er dis

turbe

d

Witnes

s

Offend

er See

n

Anythi

ng le

ft at s

cene

by of

fende

r

Fingerp

rint Id

ent

Vehicl

e stol

en in

the c

rime

Burglar

y in P

rogres

s

DNA Iden

t

Offend

ers ve

hicle

sighte

d

Suspe

ct de

scrip

tion r

ecord

ed

Footw

ear Id

ent

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%

40.00%

Percentage Frequency for Completed and Attempted Burg-laries

Completed BurglariesAttempted Burglaries

0 1 2 3 4 5 6 70.00

10.00

20.00

30.00

40.00

50.00

60.00

70.0057.69

24.88

9.414.53

2.35 0.88 0.20 0.04

Percentage of full burglaries by number of solvability factors

Most burglaries have no solvability factors present.

372 solved residential burglaries had no solvability factors present. Sample of 62 reviewed.

Consp

iracy

Cha

rges

Suspe

ct na

med by

victi

m

CCTV Pres

ent

Unkno

wn

Witnes

s pres

ent

Forens

ic Mate

rial P

resen

t

Stolen

Prop

erty r

ecov

ered

Intell

igenc

e0

5

10

15

20

2521

12

8 7 6 52 1

Frequency of Factors Associated with Case Solution Where No Solvability Factors are Present

It is possible to predict the outcome of case dependent on presence of solvability factors. Predictive accuracy would be enhanced if suspect named variable were added, conspiracy charges removed from sample and each variable were statistically weighted.

Wind

sor a

nd M

aiden

head

Brackn

ell Fore

st

Wes

t Oxfo

rdshir

e

Wok

ingha

m

Chilter

n and

Sou

th Buc

ks

Cherw

ell

Wes

t Berk

shire

Readin

g

Aylesb

ury V

ale

Milton K

eyne

s

Oxford

South

and V

ale

Slough

Wyc

ombe

455055606570

Percentage of Burglaries with one or more solvability factors by police area

The presence of solvability factors in burglaries is not uniform

Burglaries In Progress

• 5.59 Reported Burglaries in Progress in TVP per day

• 6.11% result in an arrest at or near scene.

• 4% daytime and 7% nighttime.

01000200030004000500060007000 6119 5745

374

Burglaries in Progress - Arrests Made

Just 6.11% result in an arrest in immediate response to the initial call

South

and V

ale

Brackn

ell Fore

st

Readin

g

Cherw

ell

West B

erksh

ire

Slough

Windso

r And

Maid

enhe

ad

Wycom

be

Milton K

eyne

s

Aylesb

ury V

ale

West O

xfords

hire

Chilter

n and

Sou

th Buc

ks

Oxford

Woking

ham

Out of

Force

0

1

2

3

4

5

6

7

8

9 8.3

7.2 7.26.8

6.4 6.3 6.1 6.15.6 5.6 5.6 5.4

4.8 4.8

0.0

Percentage of Burglaries in Progress with an arrrest by LPA

The arrest rate following burglaries in progress is not uniform across police areas.

<1 Minu

te

1 minu

te

2 minu

te

3 minu

te

4 minu

te

5 minu

te

6 minu

te

7 minu

te

8 minu

te

9 minu

te

10 m

inute

11 m

inute

12 m

inute

13 m

inute

14 m

inute

15 m

inute

16 m

inute

17 m

inute

18 m

inute

19 m

inute

20 m

inute

21 m

inute

22 m

inute

23 m

inute

24 m

inute

25 m

inute

26 m

inute

27 m

inute

28 m

inute

29 m

inute

> 29 m

inutes

0

5

10

15

20

25

Percentage of Arrests Made at Burg-laries in Progress by the Minutes to

the Arrival of First Unit on Scene

The percentage likelihood of capture does not decrease with the passage of time.

1 to 3 Units

4 to 6 units

7 to 9 units

10 to 13 units

13 to 15 units

16 to 18 units

19 to 21 units

More than 21

units

0

5

10

15

20

25

30

35

40

45 Percentage of arrests made by number of units attending

The optimum number of units to send to a burglary in progress is 19 to 21.

Predictor Odds of Making an Arrest (OR)

Helicopter Attending 66%*Dog Unit Attending 41%**Number of Units Attending 13%***Number of Officers Attending 5%**Sergeant Attending 4%Time to arrive 0%

Conclusions

• Once interaction effects have been taken into account those factors that most strongly predict arrest remain deployment of the helicopter and the number of units deployed.

• For every additional officer the likelihood of making an arrest increases by 6%.

• Deploying more units is more effective than just deploying officers – better to send 2 single crewed units than 1 double crewed. For every additional unit the odds of making an arrest increases by 13%.

• The attendance of dog units is correlated with arrest, but is masked by the effect of number of officers.

• The impact of Sergeant attendance is not statistically significant.

• Burglary is hard to solve. Most burglaries have no solvability factors. The most powerful solvability factors occur infrequently.

• The recovery of forensic material is more powerfully correlated than expected, especially for completed burglaries.

• Solved attempted burglaries are more strongly correlated with burglaries in progress, witnesses and the offender being disturbed.

• Solved full burglaries are more strongly correlated with forensic recovery.

• It is possible to adopt a case screening model based on the presence of solvability factors.

• This is now ready for an RCT to test a case screening approach.