another one soon after: for example, it might not take long for one
gang to retaliate against another. On other occasions it may take
much longer for knock-on effects to emerge. In the mid-1990s,
epidemiologist Charlotte Watts worked with the World Health
Organization ( ) to set up a major study of domestic violence
against women.[7] Watts had trained as a mathematician before
moving into disease research, focusing on . As her work on
developed, she started to notice that violence against women was
influencing disease transmission because it affected their ability to
have safe sex. But this revealed a much bigger problem: nobody
really knew how common such violence was. ‘Everybody agreed that
we needed population data,’ she said.[8]
The study was the result of Watts and her colleagues
applying public health ideas to the issue of domestic violence. ‘A lot
of previous research treated it as a police issue or focused on
psychological drivers of violence,’ she said. ‘Public health people ask,
“What’s the big picture? What does the evidence say about individual,
relationship and community risk factors?”’ Some have suggested that
domestic violence is completely context or culture specific, but this
isn’t necessarily the case. ‘There are some really common elements
that consistently come out,’ Watts said, ‘like exposure to violence in
childhood.’
In most of the locations in the study, at least one in four
women had previously been physically abused by a partner. Watts
has noted that violence can follow what’s known in medicine as a
‘dose-response effect’. For some diseases, the risk of illness can
depend on the dose of pathogen a person is exposed to, with a small
dose less likely to cause severe illness. There’s evidence of a similar
effect in relationships. If a man or woman has a history involving
violence, it increases the chance of domestic violence in their future
relationships. And if both members of the relationship have a history
of violence, this risk increases even further. This isn’t to say that
people with a history involving violence will always have a violent
future; like many infections, exposure to violence won’t necessarily
lead to symptoms later on. But like infectious diseases, there are a