As of July 2022, over 500 million people worldwide have contracted the SARS-CoV-2 virus, resulting in over 6 million COVID-19–related deaths [1]. Despite the remarkable and ongoing effort to inoculate the world population (over 12 billion vaccine doses have been administered so far), the rapidly evolving virus continues to spread at alarmingly high rates. Even affluent countries like Canada—a G7 member with over 83% of the population fully vaccinated—are struggling to contain the spread, with case and hospitalization numbers reaching all-time highs in the winter of 2022 [2,3]. With governments gradually lifting restrictive measures and reopening borders, it is critical that, in addition to getting vaccinated, individuals continue to follow nonpharmaceutical interventions—including wearing face masks, physical distancing, staying home when ill, and avoiding crowded indoor spaces—to limit the spread of this highly transmissible virus, especially as newer more transmissible variants continue to emerge [4-7].

Mandates and government-imposed restrictions are important policy tools for limiting the spread of COVID-19, but they are insufficient on their own and must be complemented by softer interventions designed to increase compliance with public health guidelines. Convincing citizens to freely adhere to social distancing, masking, and other preventive behaviors requires persuasive communication going beyond providing information on the risks of the pandemic. Public health organizations and governments need to understand how to best frame messages to effectively appeal to different audiences [8].

The primary objective of this study was to empirically test the effectiveness of message framings emphasizing a set of carefully selected persuasive appeals at improving people’s intentions to engage in health protective behaviors. Another aim of the study was to characterize the target audience most susceptible to respond positively to the persuasive appeals. The findings are intended to guide the design and development of public health campaigns in Canada.

In the past year, numerous studies have investigated the impact of various persuasive appeals on people’s attitudes and intentions around COVID-19–related behaviors. The studies varied in their methods and procedures and produced mixed results. Messages using prosocial, altruistic, other-focused, or community-focused appeals were generally more persuasive than messages using self-interested, self-protective, or threatening appeals [9-16]. Likewise, gain-framed messages were typically more effective than loss-framed messages [17,18], although at least one study found the opposite result [19]. Moreover, messages invoking social norms do not seem to be particularly effective [20,21].

In a comprehensive analysis, Pink and colleagues [21] tested 56 short messages using a wide range of framings, including some of the appeals mentioned above. They found no consistent effects for any of the tested messages. Nevertheless, a message using a reciprocity appeal performed the best in three of their five studies.

The present research adds to this body of work by testing the effectiveness of five appeals (deontological moral frame, empathy, goal proximity, identifiable victim, and reciprocity) at improving people’s intentions to adhere to public health measures. This study differs from prior work in at least two important aspects. First, the pandemic context at the time of our study (early March 2021) is unlike that characterizing the early stages of the pandemic when most previous studies were conducted. At the time of our study, there had been over 880,000 confirmed COVID-19 cases in Canada, including over 22,000 deaths. Vaccine supply was limited with just over 2 million doses administered by March 3, 2021 [2]. Although the daily COVID-19 activity had been declining from mid-January through mid-February, it has leveled off since. The 7-day average was under 3000 new cases a day nationwide, but variants of concern (B.1.1.7 and B1.351) had emerged [22]. Masking in public places was mandated in most jurisdictions, and the public was advised to limit travel and minimize contact with people outside of their household [22]. The difference in context alone may result in notable differences in how people process and respond to various persuasive messages.

Previous experiments have largely neglected the role of baseline attitudes and intentions when testing for differences between messages. In contrast, we expected baseline intentions to have a significant impact on how people respond to persuasive messages. People who are highly compliant to begin with have little room left for improvement. Thus, we expected the effect of persuasive appeals to be stronger among those with relatively lower baseline intentions. This is significant because those who are less compliant with public health measures are a critical target for behavior change.

This study focused on the impact of five persuasive appeals: deontological moral frame, empathy, identifiable victim, goal proximity, and reciprocity. Deontological moral frames are frequently encountered in the current public discourse; they appeal to the sense of duty and responsibilities we have to our families and communities [23]. Prior research suggests that agents making deontological judgments are perceived to be more trustworthy than agents making utilitarian judgments [24,25], even when they are not actually more trustworthy [26]. Moreover, research using machine learning found that moral identity is a strong predictor of adherence to public health measures [27]. Thus, we expect persuasive appeals that use deontological moral frames to help increase adherence to public health measures.

Empathy—understanding and feeling concerned for vulnerable others—has been found to increase altruism and caring, and to motivate helping behavior [28-30]. Thus, inducing empathy by highlighting that the sick, elderly, and immunocompromised need our help is expected to increase adoption of health protective behaviors [13,15].

Goal-proximity appeals emphasize that better days are approaching. This is important because people’s motivation to comply with public health advice has declined since the pandemic’s early days. A Gallup study tracking social distancing behaviors found that the percentage of Americans practicing social distancing dropped steadily over time, from 75% in April 2020 to 38% in March 2021 [31]. A drop in motivation over the course of goal pursuit is not uncommon when pursuing goals with no clear end states or when the tasks required to achieve the goal are difficult [32]. Fortunately, motivational strength tends to increase as the distance to the goal decreases. The goal-gradient hypothesis holds that people apply more effort and persistence as they get closer to a goal’s end state [33-37]. The third message tested in this study relies on this motivational property.

The fourth message relies on the persuasive power of identifiable victims. The identifiable victim effect refers to people’s propensity to offer more help to specific, identifiable victims rather than to anonymous, statistical victims [38-40]. This effect has been attributed to the fact that identifiable victims evoke more powerful emotional responses than statistical victims [38,41]. The identifiable victim effect also arises because people believe their contribution will have a greater impact on an identified victim than on a large group of unidentified victims [39].

Our fifth message relies on the principle of reciprocity. According to Cialdini [42], “all societies subscribe to a norm that obligates individuals to repay in kind what they have received” (page 76). The reciprocity code is not limited to gifts and favors but also includes concessions, whereby people are more likely to make concessions to those who have made concessions to them [43,44]. Accordingly, our reciprocity message emphasizes the sacrifices health care workers are making to help and protect us, and asks that we return the favor by adhering to health protective behaviors.

We expect persuasive communication to have a greater impact among individuals who have lower initial intentions to adhere with public health measures. This is because individuals who have high initial intentions have little room left for improvement; that is, they are already persuaded and further exposure to persuasive communication is unlikely to change their intentions. From a campaign planning perspective, it is important to identify who these individuals might be so that the messages can be efficiently targeted.

The existing literature points to significant variability in the levels of adherence to public health measures [45-52]. A recent review of 29 empirical studies concluded that greater adherence to public health measures is reliably associated with being older, identifying as female, trusting governments, perceiving COVID-19 as a threat, and accessing information through traditional news media [50]. Variability in uptake of public health behaviors was also linked to differences in political ideology [51,52] and perceived responsibility for others [53]. In this study, we measured these characteristics and examined their associations with baseline intentions.

A representative sample of adult Canadian residents with respect to age, ethnicity, and province of residence was recruited by the research firm Critical Mass between March 3 and March 6, 2021. A description of the study was posted on Lucid Marketplace, a third-party platform that maintains an online research panel of 15 million verified users. Users from Canada were invited to visit a screening page assessing demographic and geographic variables. Target quotas for province of residence, age, gender, and ethnicity were set to obtain a demographically representative sample based on the 2016 census data (see Table S1 in Multimedia Appendix 1 for details on the quota system).

Upon consenting in writing, participants reported on their intentions to engage in a set of prevention behaviors over the coming weeks (T1). They were then randomly assigned to an active control or one of five persuasive appeal conditions (control vs deontological vs empathy vs goal proximity vs reciprocity vs identifiable victim) and reported on their intentions to engage in the same set of prevention behaviors a second time (T2). This design allowed us to examine whether the effectiveness of persuasive appeals varies as a function of initial prevention intentions. Finally, participants completed a series of questions assessing potential correlates of prevention intentions. These included measures of political orientation, trust in institutions, perceived threat of COVID-19, and perceived responsibility toward others.

This study was approved by the University of Calgary Conjoint Research Ethics Board (REB21-0173) and was conducted according to the principles expressed in the Declaration of Helsinki.

Index variables for intentions to engage in prevention behaviors (pre- and posttreatment) were created by averaging across six items: (1) Limit my physical contact with others when possible, (2) Completely avoid any unnecessary physical contact with others (eg, hugging or handshakes), (3) Avoid crowded indoor spaces, (4) Wear a mask when I leave the house, (5) Wash my hands as much as possible, and (6) Stay home when mildly sick. These items were measured on 100-point sliding scales (0=strongly disagree, 50=neither agree nor disagree, 100=strongly agree).

Persuasive appeals were manipulated using promotional flyers ostensibly distributed by the Public Health Agency of Canada. In the control condition, the flyer contained a simple list of what participants can do to help prevent the spread of COVID-19. In each of the five persuasion conditions, the flyer contained the same basic information and a unique persuasive appeal (see Figure 1 for an example and Figures S1-S5 in Multimedia Appendix 1 for the remaining flyers). The wording of the messages is shown in Textbox 1.

Trust in various institutions (politicians, civil servants, public health officials, physicians, other health care providers [eg, nurses, pharmacists], scientists, journalists, and pharmaceutical companies) was measured using eight items (α=.91) on 100-point sliding scales (0=do not trust at all, 100=trust completely).

Perceived COVID-19 threat was measured using four items (α=.89) adapted from previous research [11]. A sample item is: “To what extent are you afraid of contracting COVID-19 because of the consequences for you personally/your community?” (0=not at all, 50=to a moderate extent, 100=to an enormous extent).

Perceived responsibility toward others was assessed using four items (α=.94) adapted from previous research [18]. A sample item is: “I owe it to my family to do whatever I can to stop the spread of COVID-19” (1=strongly disagree, 7=strongly agree).

Finally, political orientation was measured using the following item: “If you think about your own political views, where would you classify your views on this scale?” (1=very liberal, 7=very conservative).

First, we sought to address the broad question: does exposure to messages using persuasive appeals improve intentions to engage in prevention behaviors more than exposure to the control message? Given the structure in our data (each participant provided two sets of ratings), we fitted a linear mixed effects model (estimated using maximum likelihood) with intention to engage in prevention behaviors as the outcome variable; random intercepts for participants (id); and fixed effects for appeal condition, time of rating, and their interaction. In this analysis, the P values were estimated via t-tests using the Satterthwaite approximation to degrees of freedom. Effect sizes for the fixed effects are indicated by the standardized regression coefficients (β) and their 95% CIs.

We performed a series of moderated regressions (estimated using ordinary least squares [OLS]) to investigate whether the effectiveness of persuasive appeals varies as a function of baseline prevention intentions. We used change in intentions as the outcome variable, persuasion appeal as a binary predictor, and baseline intentions as a continuous moderator.

To help characterize the target audience, we examined the association of baseline intentions with demographic variables, including age, gender, ethnic background, education, and geographic region, as well as attitudinal variables such as perceived COVID-19 threat, perceived responsibility toward others, trust in institutions, and political orientation.

We fitted a linear model (estimated using OLS) using all predictors. The continuous predictors (age, threat, responsibility, trust, and political orientation) were mean-centered and the categorical predictors were dummy-coded. The ethnic background variable was constructed by recoding the original ethnicity variable into a binary variable (0=ethnic majority, 1=ethnic minority). Education was modified by combining the “less than high school” and “high school” categories into a single “high school or less” category, which served as the baseline group in the analysis. The region variable was constructed by collapsing the Newfoundland and Labrador, Nova Scotia, New Brunswick, and Territories categories in the province variable into a single “Maritimes and Territories” category. Ontario was set as the baseline category for the five-level region variable and female was set as the baseline category for the three-level gender variable.

Data analysis was performed using the statistical program R version 4.0.2 [54], and the level of statistical significance was set at α=.05.

A total of 7079 respondents visited the screening page. Of those, 3746 qualified for the main study based on the quota requirements. Of the qualified respondents, 78 failed to complete the survey, resulting in a final sample of 3668 participants (see Table 1 for sample characteristics). Those who failed to complete the survey were demographically similar to those who completed the survey, but were predominantly from the provinces of Quebec (40%) and Nova Scotia (19%) (see Table S1 in Multimedia Appendix 1).

The results of the fixed factors in the mixed effects model are summarized in Table 2 (random effects: σ²=18.90, τ_00id=282.54, intraclass correlation coefficient=0.94, N_id=3668, observations=7331, marginal R²=0.006, conditional R²= 0.938). Prior to exposure to the persuasive appeals, participants in all conditions reported similarly high intentions to engage in prevention behaviors. Prevention scores at T1 did not differ significantly between any appeal condition and the control condition, as shown in Table 2 (P values for deontological, empathy, goal proximity, reciprocity, and victim are all greater than .05). This confirmed that random assignment produced groups with equivalent baselines. Furthermore, exposure to a reminder message about prevention behaviors (ie, control condition) increased participants’ intentions to engage in prevention behaviors (see Time [T2] variable in Table 2). Additionally, exposure to a persuasive message using an empathy appeal resulted in a larger increase in intentions to engage in prevention behaviors relative to the control message (Table 2).

Exposure to messages using other types of appeals (deontological, goal proximity, reciprocity, and victim) produced positive changes in intentions to engage in prevention behaviors (see Table 3), but these changes did not differ in magnitude from those produced by exposure to a simple reminder message (all P>.05). Figure 2 shows the estimated marginal means for each group and their 95% CIs.

The preceding analysis suggested that, apart from empathy, the use of persuasive appeals does not improve intentions to engage in prevention behaviors beyond a simple reminder message. However, we expected the effectiveness of persuasive appeals to vary according to people’s initial dispositions. Persuasive appeals are likely effective when baseline intentions are relatively low, but may have a limited impact when baseline intentions are so high that there is little room for improvement. Results from the moderated regressions were consistent with our expectations (see Table 4). The appeal×baseline intentions interaction was statistically significant for all but the goal-proximity appeal, suggesting that the effectiveness of the deontological, empathy, reciprocity, and identifiable victim appeals indeed depends on the level of initial intentions.

We followed up with floodlight analyses [55] of each significant interaction. As shown in Figure 3, the conditional effect of seeing a deontological appeal was significant only among participants who had a score of 85.5 or below on the initial intentions measure (30.2% of participants; mean 66.4). In other words, people with lower baseline intentions increased their intentions to engage in prevention behaviors more after seeing a message featuring a deontological appeal than after seeing a message featuring a simple reminder. In contrast, those with high baseline intentions (higher than 85.5; 69.8% of participants; mean 96.2) did not differ significantly in how much they changed their intentions when they saw a message featuring a deontological appeal or a message featuring a reminder.

We observed similar patterns with the other appeals. The conditional effect of empathy was significant only among participants scoring 90.1 or lower on initial intentions (39.5% of participants; mean 71.5), the conditional effect of reciprocity was significant only for those scoring 87.8 or lower on initial intentions (44.1% of participants; mean 68.7), and the conditional effect of identifiable victim was only significant for those scoring 84.8% or lower on initial intentions (29.3% of participants; mean 65.7).

The moderation analysis implied that a public health campaign using persuasive appeals would be most effective when targeting individuals with lower baseline intentions: but who might these individuals be?

The regression model using all demographic and attitudinal predictors explained a statistically significant and substantial proportion of the variance (R²=0.51, F_{16, 3415}=224.2, P<.001, adjusted R²=0.51). As shown in Table 5, baseline intentions increased with age, perception of COVID-19 threat, perceived responsibility, and trust in institutions. Conversely, baseline intentions decreased with political conservatism, were lower for males relative to females, and were lower in the Prairies compared to Ontario. Neither education level nor ethnic background was significantly uniquely associated with baseline intentions to engage in prevention behaviors.