Measuring perceptions of synergistic circulatory disease risk due to smoking and the oral contraceptive pill

There is evidence that the oral contraceptive pill (OCP) and smoking contribute independently to risk of circulatory disease. There is mixed evidence that the combined risk may be greater than the sum of these factors operating in isolation. Little is known about how the general population views the risks from OCP use, singly and in combination with smoking. Previous attempts at assessing whether the public views risks as operating synergistically have generally found evidence for subadditive models, where the combined risk is less than the sum of factors operating in isolation. However, concerns have been expressed over the validity of the measures of risk perception used. Therefore, this study used three distinct methods of measurement to assess the extent to which 241 undergraduate students perceive the risks of smoking and the OCP separately and combined, for circulatory disease. For all three methods, respondents read each of four vignettes describing information about a woman's risk factors (with high and low levels of both OCP and smoking), and then estimated risk of circulatory disease using one of the three risk measures. The three measures produced similar ratings. Consistent with the epidemiological evidence, information about smoking had more impact on estimates of overall risk than did information about the OCP For all three measures, responses were consistent with an additive model of risk from smoking and the OCP. This convergence of results from different methods suggests that all three methods of measurement employed, which all had a large number of response options, may be valid.