course, this doesn’t mean broken windows policing has no effect.
There’s evidence that the presence of things like graffiti and stray
shopping trolleys can make people far more likely to litter or use an
out-of-bounds thoroughfare.[91] This suggests that minor disorder will
spark other minor offences. The effect seems to work the other way
too: attempts to restore order – like picking up litter – can prompt
others to tidy up as well.[92] But it’s quite a leap to go from such
results to the conclusion that arrests for misdemeanours can explain
a massive drop in violence.
So what caused the decline? Economist Steven Levitt has argued
that expanded access to abortion after 1973 played a role. His theory
goes that this meant there were fewer unwanted children, who would
have been more likely to be involved in crime when they grew up.
Others blame childhood exposure to leaded petrol and lead paint in
the mid-twentieth century, which caused behavioural problems later
on; when the level of exposure declined, so did crime. In fact, a
recent review found that, in total, academics have proposed twenty-
four different explanations for the decline in US crime during the
1990s.[93] These theories have attracted plenty of attention – as well
as criticism – but the researchers involved all acknowledge that it’s a
complicated question. In reality, the drop in crime was likely the result
of a combination of factors.[94]
This is a common problem with outbreaks that occur on long
timescales. If we intervene in some way, we might have to wait a long
time to see if it has an effect. In the meantime, there might be lots of
other changes going on too, making it hard to measure exactly how
well our intervention works. Similarly, it can be easier to focus on the
immediate effects of a violent event, rather than investigate longer-
term harm. Charlotte Watts has pointed out that domestic violence
can be transmitted across generations, with affected children
becoming involved in violence as adults. However, these children can
often be forgotten when discussing interventions. ‘We need to think
about support for children growing up in households where there is
domestic violence,’ she said.
Historically, it’s been difficult to analyse intergenerational
transmission given the timescales involved.[95] This is where public