Outdoor Lighting and Crime - Amper

Zealand
(Not
shown in
figures)
Population
1970 2001 0.980
0.960
0.983
0.966
For each of the three countries studied in Figures 1 to 3, real expenditure on police has
increased over recent decades. For example, allowing 1.726 for the total inflation, the real per
capita expenditure increase for all US police forces combined over the period 1980 to 1999
(BJS 2002b) was a factor of 2.016. The bulk of this expenditure is likely to have gone into
increasing police numbers rather than into more and better equipment and training (Greenberg
1983).
Doubling of police numbers represents a compounding 10% increase repeated about 7 times.
Using Marvell and Moody’s (1996) estimate of the effect of a 10% increase in police
numbers, a doubling of police would reduce crime to (0.971) 7 , ie 0.814, or a reduction of
18.6%. Goodman’s (2002) first estimate of the same effect is more appropriate here than his
second estimate. The first estimate indicates a reduction to (0.989) 7 or 0.925, ie a reduction of
7.5%.
Had there not been progressive real increases in police force expenditure in the countries
studied, some notional progressive increases would have occurred in the crime rates instead.
The overall effect of this would again be to improve the correlation with skyglow a little more
than with population. In the case of the USA, if real police expenditure had remained at the
1980 level, the UCR crime rate value for 2001 would have been nearly 30% higher than is
shown in Figure 3.
Australia, UK and USA all increased their prison populations substantially in the last decades
of the twentieth century. As with the effect of police, criminologists differ about the effect of
incarceration on the crime rate. Even if the deterrent effect of incarceration is discounted, the
balance of opinion seems to be that incapacitation of offenders does have a substantial effect
in reducing overall crime. Langan (1994) concluded that the increase in US prison population
from 1975 to 1989 reduced reported and unreported crime by between 10 and 15%. Hayward
and Izumi (1996) collected estimates by others of how many serious crimes per prisoner per
year are avoided by incarceration: the range was 12 to 187. Marvell and Moody (1994)
reached a conservative estimate of 17 and a more likely value of 21 crimes prevented per
prisoner per year. The effect of this on the crime rate is like that of increased police
resources: in its absence, crime would be worse than it is and again the effect would be a
steeper rise in recent years and a better correlation with lighting.
Using Marvell and Moody’s value of 21 crimes per prisoner per year, had their been no
increase in incarceration in the USA since 1980, the UCR crime rate value for 2001 would
have been nearly 70% higher than is shown in Figure 3. Adding this to the effect of no extra
police, the net result would be a 2001 crime rate value about double that shown in Figure 3.
The case for a high correlation of lighting and overall crime is a lot stronger than Figure 3
indicates.
1
1
18