Outdoor Lighting and Crime - Amper

On the assumption that roads and paths had been cleared of snow and that the snow was
contaminated by vehicle exhaust particles, the effective terrain reflectance was estimated to be
0.7 for Minneapolis and 0.6 for St Louis. The light energy loss values were divided by 2.56
and 2.04 respectively (from Table 4) to give values more likely to be representative of nosnow
conditions. In the case of Buffalo, Denver and Kansas City, the effective terrain
reflectance was thought more likely to be about 0.3 at the time of measurement. The factor
for light energy loss correction to no-snow conditions for these three cities was therefore 1.52.
The corrected data points were closer to the notional trend line of Figure 8, but still to its right
(brighter) side. The corrected light energy losses for Minneapolis, St Louis, Buffalo, Denver
and Kansas City are shown in parentheses in Tables 5 and 6.
The linear regression analysis was repeated for the plot values of Figure 7 after the corrections
to give no-snow conditions were applied to the five cities. The slope became negative and
larger, -0.102, but was still not significantly different from zero (r 2 = 0.052, t = 1.016, 19 df).
Neither Figure 7 nor its version corrected to no-snow conditions (not shown) represents a
year’s results accurately, as snow was present only for part of the year. Presumably they do
represent their respective parts of the year well enough, and the whole year’s results would be
an appropriate mix of the two parts, weighted according to the fraction of days with snow
cover. Clearly, the regression line slope for a combined result would still not be significantly
different from zero.
The sample size for Figure 7 is the maximum set by the available source of light energy loss
data. The choice of crime data is less constrained, and may have a large effect on the
results. 61 Although the 1997 UCR report is still available (FBI 1997), it was not used as it has
no data for Buffalo, Kansas City, Las Vegas, Philadelphia and St Louis. These five cities
were in the eight brightest of the 21 and their absence would have biased and degraded the
results. Given the nature of the hypothesis, it seems quite reasonable to use crime data for a
year (1998) that started ten or eleven months after the satellite measurements of light energy
loss.
61 Other variables may also have an effect. For example, the latitude effect on crime
mentioned in Section 2.4 applies between countries, with countries having a smaller mean
latitude tending to have a higher victimisation percentage V, given by V = 40.7 – 0.4 L, where
L is the mean latitude in degrees (Walker, Wilson, Chappell and Weatherburn 1990). During
an initial attempt at Figure 7, a 60% larger but non-significant within-country latitude-effect
regression line slope was found for 1999 UCR data for US Metropolitan Statistical Areas. No
latitude effect was apparent using the 1998 UCR city data obtained subsequently as more
appropriate for Figure 7. Walker et al. related between-country effects in general to the
amount of time individuals spent outdoors in the evening, and the latitude effect to an
informal curfew imposed by cold and wet conditions at higher latitudes. A present extension
of these reasons is that the degree of encouragement for individuals to be outdoors at night
would presumably also be increased by the extent of artificial lighting, thereby increasing
opportunities for crime.
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