Parsing susceptibility and severity dimensions of health risk perceptions.

Risk perceptions, an important determinant of positive behavioral change, are often conceptualized as an additive or multiplicative index of two concepts: susceptibility to and severity of a health risk. Susceptibility is the possibility of experiencing a health risk, whereas severity is its seriousness or harmfulness. This article challenged the current theorization of risk perceptions. To demonstrate the differential perceptions of susceptibility and severity, two self-report studies (N = 70, each) and one reaction time study (N = 476) provided data on 50 health conditions that varied on several risk characteristics (e.g., prevalence, personal experience). Results showed that susceptibility and severity were two distinct, inversely related concepts. Perceived susceptibility and severity varied by risk characteristics, mainly prevalence (i.e., how common a health risk was perceived to be). Self-report data showed that a progressive increase in perceptions of a health risk prevalence rates was associated with an increase in susceptibility and a decrease in severity (and vice versa). Reaction-time data mirrored this pattern and showed these differential perceptions of susceptibility and severity were highly accessible, as evident by fast reaction times. Several individual differences (e.g., optimism) emerged as significant predictors of risk perceptions and their accessibility. Theoretical and practical implications are discussed.