The Rules of Contagion

performing such actions, it’s much easier to get them to act. ‘It’s a
light touch nudge for an easy to accomplish, low-cost behaviour.’
This creates a challenge for marketers. An advertising campaign
might generate a lot of likes and clicks, but this isn’t quite the
behaviour they’re interested in. They don’t just want people to interact
with their content; they eventually want people to buy their product or
believe in their message. Just as people with more followers won’t
necessarily generate larger cascades, content that’s more clickable
or shareable won’t automatically generate more revenue or advocacy.
When we’re faced with a new disease outbreak, there are
generally two things we want to know. What are the main routes of
transmission? And which of these routes should we target to control
the infection? Marketers face a similar task when designing a
campaign. First, they need to know the ways someone can be
exposed to a message; then they need to decide which of these
routes to target. The difference, of course, is that whereas health
agencies spend money to block the crucial paths of transmission,
advertising agencies put money into expanding them.
Ultimately, it’s a question of cost-effectiveness. Whether we’re
dealing with a disease outbreak or marketing campaign, we want to
find the best way to allocate a limited budget. The problem is that
historically it’s not always been clear which path leads to which
outcome. ‘Half the money I spend on advertising is wasted; the
trouble is I don’t know which half,’ as marketing pioneer John
Wanamaker supposedly once said. [79]
Modern marketing has tried to tackle this problem by linking the
ads people see to the actions they take afterwards. In recent years,
most major websites have employed ad tracking; if companies
advertise on them, they know if we saw the ads as well as whether
we browsed or bought anything afterwards. Likewise, if we take an
interest in their product, a company can follow us around the internet,
showing us more ads.[80]
When we click on a website link, we often become the subject of a
high-speed bidding war. Within about 0.03 seconds, the website
server will gather all the information they have about us and send it to