The Economist took a look at adverts that aim to shock and awe:

• Gory adverts, such as those focused on the number of children who die as a result of speeding, leave a longer lasting impression on viewers than non-gory ones.
• However they are less effective at changing behaviour, possibly because extremist ads showcase threats that seem farfetched.
• Positive ads that encourage people to quit smoking, are, for example, more effective than negative ads that try to scare smokers with images of tumors.
• Cash strapped governments and NGOs may increase the use of shock ads, however, since they are more likely to be shared on social media and thus reach a wider audience.

Read more here.

Source: The Economist