Do People Believe Combined Hazards Can Present Synergistic Risks?

Abstract

The risk attributable to some hazard combinations can be greater than the sum of the risk attributable to each constituent hazard. Such "synergistic risks" occur in several domains, can vary in magnitude, and often have harmful, even life-threatening, outcomes. Yet, the extent to which people believe that combined hazards can present synergistic risks is unclear. We present the results of two experimental studies aimed at addressing this issue. In both studies, participants examined synergistic and additive risk scenarios, and judged whether these were possible. The results indicate that the proportion of people who believe that synergistic risks can occur declines linearly as the magnitude of the synergistic risk increases. We also find that people believe, despite scientific evidence to the contrary, that certain hazard combinations are more likely to present additive or weakly synergistic risks than synergistic risks of higher magnitudes. Furthermore, our findings did not vary as a simple function of hazard domain (health vs. social), but varied according to the characteristics of the specific hazards considered (specified vs. unspecified drug combinations). These results suggest that many people's beliefs concerning the risk attributable to combined hazards could lead them to underestimate the threat posed by combinations that present synergistic risks, particularly for hazard combinations that present higher synergistic risk magnitudes. These findings highlight a need to develop risk communications that can effectively increase awareness of synergistic risks.

Using risk model judgements to better understand perceptions of synergistic risks

“…Such an intuitive understanding of synergistic risk has been identified in previous research (see Dawson, Johnson & Luke, 2012a) and, therefore, might also offer a partial explanation for other evidence indicating that individuals may hold synergistic models of risk for the radon-tobacco combination (Eiser et al, 1995;Hampson et al, 2000). However, this interpretation raises the additional question of why a majority of participants did not employ this intuitive synergistic risk model when making a judgement for the aspirin-clopidogrel combination?…”

“…As Condit and Shen identified (p. 122), the provision of numerical data may have framed the judgement task as a mathematical problem and, therefore, induced participants to employ numerically reasoning to 'solve the problem'. Previous research by Dawson, Johnson and Luke (2012a) shows that individuals who reason numerically when formulating a judgement about the risk attributable to combined factors often arrive at an additive risk model because they believe that the numerical risks 'add up' (i.e. 20% + 20% = 40%) consistent with the notion of 'adding' (i.e.…”

“…More recently, researchers have employed alternative methods, such as examining 'possibility judgements' and 'articulated reasoning' to assess individual's judgements and understanding of synergistic risks (see Dawson, Johnson, & Luke, 2012a, 2012c. One innovative approach, introduced by Condit and Shen (2011) in a study concerning public understanding of geneenvironment interactions, required participants to provide risk model judgements rather than risk magnitude estimates.…”

“…A clear concern is that if individuals underestimate the threat posed by synergistic risks they will not be motivated to adopt appropriate precautionary behaviours or to demand/support political, social, and economic action to address these issues (Dawson, Johnson, & Luke, 2012a, 2012cFrench, Sutton, Kinmonth, & Marteau, 2006). Similarly, where policy-makers and regulators do not recognise that certain combined factors present synergistic risks, there is a concern that they may fail to implement policies and strategies that are proportionate to the risks (Berenbaum, 1989;Cogliano, 1997).…”

Growing Pains: How Risk Perception and Risk Communication Research Can Help to Manage the Challenges of Global Population Growth

“…For example, when an expanding population increases its consumption of both fossil fuels and natural land, these factors can interact to present a synergistic risk of biodiversity loss . It is, therefore, of some concern that evidence suggests that many individuals may have difficulty understanding specific synergistic risks . Finally, the size and effects of global population growth cannot be predicted with accuracy, and these uncertainties may present challenges for risk communicators.…”