Estimating offence
times from victim
reports
Matt Ashby and Kate Bowers
The problem of aoristic crime
If you get home to find your
house has been burgled,
will you be able to tell the
police when it happened?
The problem of aoristic crime
Earliest possible
offence time
0900 hours
Latest possible
offence time
1200
1800
range >1 hour for 63% of commercial burglaries, median 6 hours
range >1 hour for 88% of thefts of motor vehicles, median 11.5 hours
Data
Records of 1,396 pedal cycle thefts from
railway stations, including:
•offence start and end time times
•description of investigation
•whether or not CCTV helped the investigation
Actual offence
time from CCTV
Earliest possible
offence time
0900 hours
Latest possible
offence time
1200
1800
Is 303 crimes a big-enough sample?
Median crimes per month in a London borough
Crime type
Crimes
Dwelling burglaries
Thefts … of cycles
of vehicles
from vehicles
Damage … to dwellings
to vehicles
150
39 x 12 = 468 cycle thefts
70
191
51
88
per year
Method
Start
Wr
4.73**
** p < 0.05
** p < 0.01
Method
Wr
Start
4.73**
End
3.10**
** p < 0.05
** p < 0.01
Method
Wr
Start
4.73**
End
3.10**
Mid point
1.53**
** p < 0.05
** p < 0.01
Method
Wr
Start
4.73**
End
3.10**
Mid point
1.53**
Random
0.28**
** p < 0.05
** p < 0.01
Method
Wr
Start
4.73**
End
3.10**
Mid point
1.53**
Random
0.28**
Aoristic
0.23**
** p < 0.05
** p < 0.01
Good
aoristic or random methods
Not too bad
mid-point and known-time methods
Very bad indeed
start and end methods
Thanks
British Transport Police for data
British Transport Police,
Ryan Gallagher and
Daniel Hoherd for photos