II Susceptibility as a determinant of message acceptance and behaviour change
III How to sway perceived susceptibility
IV Practice implications
--Submitted by Sophie Rosa
Perceived susceptibility can be defined as one’s estimation of his or her chances of developing a health condition or being harmed by something. [1,2] It is a key concept in many well-known health promotion and health information processing models, such as the Health Belief Model , the Risk Attitude Framework , Parallel Response Model , Protection Motivation Theory  and the Extended Parallel Process Model . In these models, perceived susceptibility is often combined with perceived severity to create the dimension of perceived threat, which is assumed to influence how health information is processed and motivates behaviour change.  This article presents how susceptibility, and its role in fear appeals, has been widely demonstrated as a significant determinant of message acceptance and behavior change.
II Susceptibility as a determinant of message acceptance and behaviour change
According to the models introduced above, for a message to be accepted and processed, individuals must have a sense of being susceptible to a given risk. For instance, Gallagher et al. (2011) reported higher acceptance of breast cancer screening messages in women with a higher level of susceptibility compared to women with lower levels of perceived susceptibility.  In adult women, perceived susceptibility to develop breast cancer is an ever present concern, with varying levels, that has been demonstrated as a predictor for detection behaviours, such as self-examinations and mammograms. [7,8] Perceived susceptibility has also been linked to a variety of other cancer prevention behaviours. [9,10,11,12] Lower levels of perceived susceptibility were associated with lower intention to engage in genetic testing and other preventive behaviours related to genetic diseases.
Current published literature offers review-level evidence and single studies that provide detail on how perceived susceptibility influences message acceptance. Moreover, this same literature demonstrates how behaviour change supports the theory that the relationship between levels of susceptibility and efficacy is a key determinant in the development of effective health messages. Efficacy is a dimension in various health promotion models that includes both response-efficacy (the belief that a given behavior change will lead to the desired outcome) and self-efficacy (the belief that one is able to adopt and maintain a new health behaviour). When both perceived threat and efficacy are high, individuals tend to adopt danger control responses such as changes in attitudes, intentions and health behaviours.  These danger control responses indicate message acceptance and integration. Such a phenomenon has been reported in eating disorders , doctor-patient interactions , smoking cessation activities  and sexual health  campaigns. On the other hand, when susceptibility and efficacy are low, a meta-analysis by Witte & Allen (2000) reported that individuals tend to adopt fear control behaviors such as denial, defensive avoidance and opposite responses. Fear control behaviours indicate message rejection.  Furthermore, when perceived threat is high and efficacy is low, individuals will also tend to reject a message and do the very opposite of the advocated behaviour. [1,19,20]
III How to sway perceived susceptibility
There are various tactics to sway the level of perceived susceptibility; namely, normalization and the use of narratives with relevant statistics, both described below.
Health communicators can aim to develop or reinforce favorable social norms to increase perceived susceptibility. Individuals may either underestimate or overestimate the prevalence of certain risk or prevalence of certain illnesses, which in turn influences their lifestyle choices. For instance, Klein & Helweg-Larsen (1980) introduced the concept of optimistic bias, defined as “people’s tendency to think their risk is less than that of their peers.” On the other hand, a literature review on drinking behaviours in college reported that students consistently overestimate their peers’ drinking levels and that informing them about the real level of drinking by their peers corrected these misperceptions and reduced alcohol consumption and alcohol-related problems. As such, health practitioners should assess their target audience’s level of perceived susceptibility and examine the true prevalence of a risk or disease, to then appropriately design their health messages to leverage the population’s magnetic pull towards the norm. Since people are naturally motivated to comply with norms, adjusting it can become a cost-effective tactic that leads to immediate results when an increase in perceived susceptibility is required. [23,24]
Narratives and statistics
Use of narratives or storytelling is an emerging area of health communication. Evidence suggests that narratives successfully increase perceived susceptibility since they do not give rise to defensive behaviors as much as statistics have been reported to do. [25,26] It also increases relevance of the messages, especially if the individual can model and relate to the narrator or key actor in the narrative. [25,26] However, recent studies show that a combination of both narratives and statistical evidence will generate a greater increase in perceived susceptibility, as opposed to narratives alone, as seen in Nan et. al (2015) with regards to perceived susceptibility to human papillomavirus (HPV).  First person narratives were also found to be more effective than third person narratives.  Along the same lines, Frank et al. (2005) demonstrated that relevance of the HPV narrative and level of identification with the character were both positively associated with perceived susceptibility. 
Susceptibility in fear appeal models
Fear appeals have garnered significant consideration in the last few decades. In 2000, Witte and Allen published a comprehensive meta-analysis on the effectiveness of fear appeals in public health campaigns indicating that greater changes in attitudes, intentions and behaviour occurred when the messages included strong fear appeals, communicated both high susceptibility and severity, and when messages contained high efficacy components.  Their results showed that well-designed fear appeals can be effective regardless of demographics and personality traits.  However, a recent series of single studies on fear appeals published in a special issue of the journal Health Communication suggested they should not be considered the best approach for every topic and audience. These findings highlight the importance of careful audience analysis to effectively manage the combination of characteristics in a message, as well as focus testing messaging strategies and materials, when using fear appeals.  Two fear appeal models noticeably emerge from the body of literature: the Extended Parallel Process Model  and the Risk Perception Attitude Framework , both described below.
Extended Parallel Processing Model
The Extended Parallel Process Model (EPPM)  integrates three earlier fear appeals models: the Fear-as-acquired Drive Model , the Parallel Process Model  and the Protection Motivation Theory.  The EPPM aims to explain why fear appeals succeed in certain cases and fail in others. It proposes that a health message must include, in an appropriate balance, two basic constructs: fear, which includes both susceptibility and severity, and efficacy, which includes both self-efficacy and response-efficacy. The balance between those two constructs in the health message will determine the type of response the individual will have: danger control (changes in attitudes, intentions and behaviors) or fear control responses (denial, defensive avoidance or pursuing the opposite of the advocated behaviour).
EPPM is the predominant model in existing fear appeal literature, and many meta-analyses have indicated that high threat and high efficacy together consistently lead to positive changes in attitudes, intentions and behavior change. [14,31,32,33] However, these meta-analyses also indicated that the EPPM should be used only when efficacy is high. The authors also highlight gaps in research about how threat and efficacy in health messages interact to lead to positive changes in attitudes, intentions and health behaviours. [14,31,32,33]
The Risk Perception Attitude Framework
The Risk Perception Attitude framework (RPA)  is an audience analysis tool that segments a target audience according to its perception of risk and its self-efficacy beliefs. It integrates both the perceived efficacy construct of the Social Cognitive Theory  and the perceived threat constructs of the Extended Parallel Process Model . However, unlike the EPPM, this model considers perceived risk and efficacy to be psychographic variables in the individual, rather than elements of the message. It also suggests that ones’ self-efficacy moderates how risk perceptions affect self-protective behaviour.
The RPA model categorizes or classifies individuals in one of four attitude groups. First, individuals with low risk perceptions and efficacy are described as having an attitude of “indifference”. They are not motivated to act nor do they perceive to have any control over their situation. As such, they will be unlikely to engage in any self-protecting or health behaviours. Second, individuals with high risk perceptions and efficacy have a “responsive” attitude. They appreciate the risk and feel they have control over their situation and health, so they are more likely to engage in self-protective and healthy behaviours. Third, individuals with low risk perceptions and high efficacy are categorized as having a “proactive” attitude. They have a strong sense of control, but it is not enough to motivate them into self-protective and health behaviours. Lastly, individuals with low efficacy beliefs and high risk perceptions fall into the category of “avoidance” attitudes. The fact that they are motivated to act but at the same time believe they will likely fail, or have no control over their situation, prevents them from engaging in self-protective and health behaviours.
The key objective of any health message, according to this model, is to move individuals towards a “responsive” attitude to maximize health and self-protective behaviours. This model’s effectiveness has been demonstrated in a variety of topics, namely healthy eating , HIV prevention , breast cancer prevention [37,38], workplace safety , food safety , avoidance of texting and driving  and diabetes awareness, management and prevention .
IV Practice implications
The available evidence clearly shows that susceptibility is a key determinant of message acceptance and behaviour change. As such, it should be used to segment audiences accordingly to maximize the effectiveness of health communication efforts. Clearly establishing whether segments of the population should be targeted with tailored messages that moderate perceived threat, perceived efficacy, or both will be more effective than messages that are not tailored to these dimensions.
Appropriate message framing
As described earlier, Gallagher et al. (2011) reported higher acceptance of breast cancer screening messages in women with a higher level of susceptibility to breast cancer compared to women with lower levels.  The authors further describe the effect of message framing on the intention to get screening and actually undergoing screening in both high and low perceived susceptibility groups. In their analysis, the authors argued that loss-framed messages were more likely to increase screening behaviours in high perceived susceptibility women since they would consider a potential positive diagnosis as risky. As such, the potential loss of their health and years to their lives would be strong motivators. As for women with lower perceived susceptibility, the authors suggested that the prospect of positive results is less evocative, and as such, loss-framed messaging would not be as motivating. Also, mammograms were regarded by a majority of women as an illness-detecting process, rather than a health-affirming one, making gain-framed messages less likely to motivate women. In women who view mammograms as health-affirming, gain-framed messages were more effective. 
Health communication efforts should pair strong fear appeals with equally, if not stronger, efficacy messaging. Both response- and self-efficacy are key elements in fear appeals’ effectiveness for generating meaningful changes in health and self-protective behaviors. Lack of the efficacy dimensions in fear appeals messaging strategies will likely lead to people denying the facts or threat and reacting against it, behaving in the opposite of what is advocated, adopting a defensive mechanism such as wishful thinking, or feeling a sense of hopelessness. 
Susceptibility and its role in fear appeals is a key variable in health communication efforts. To ensure evidence-based messaging strategies have impact, audience analysis should include a thorough examination of the target audience’s level of perceived susceptibility as well as their levels of both response and self-efficacy. Health practitioners should carefully consider these dimensions in the formulation of their health messages and communication tactics in order to elicit appropriate risk assessment and nurture sense of efficacy in their target population.
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