Severity and susceptibility: measuring the perceived effectiveness and believability of tobacco health warnings.

Our findings support previous evidence that pictorial HWLs are rated as more effective and believable than text-only warnings, and provide some support for the use of severe or 'grotesque' HWLs on tobacco products. Our data also suggest that HWLs should aim to increase perceived susceptibility to disease, as this was positively related to perceived message effectiveness and believability.