Facts Tell, Stories Sell? Assessing the Availability Heuristic and Resistance as Cognitive Mechanisms Underlying the Persuasive Effects of Vaccination Narratives

"...highlights potentially fruitful ways in which science should further examine whether, how, and to what extent strategic communication has the potential to change pre-existing beliefs."

Parents who turn to the internet for information on their children's vaccinations are likely to encounter vaccine-critical information that is frequently presented as personal narratives that are not based on scientific evidence. Such narratives can be persuasive, leading hesitant parents' perceptions of vaccine safety to be easily influenced toward negative attitudes. To gain insight into the mechanisms underlying the impact of vaccination narratives, research has mainly focused on affective mechanisms. However, because cognitive processes may play an important role in the formation and change of vaccination-related beliefs, this online study examined two cognitive mechanisms that might affect how people process, retrieve, and perceive information from online vaccination narratives: the availability heuristic and cognitive resistance. The purpose was to empirically test whether and how different formats impact the way in which readers process and retrieve information about childhood vaccination, and how this may impact their perceptions.

The researchers explain that, when people make decisions under uncertainty, they are often susceptible to heuristics, which can lead to numerous biases. People rely on heuristics (cognitive shortcuts) when assessing probabilities by reducing complex mental operations to simplified judgmental tasks. The availability heuristic is a mental strategy used when people estimate the probability of an event based on how easily an instance of such an event comes to mind. For example, the perceived risk of vaccine-adverse events is affected by whether it is easy or difficult to access in one's memory an instance of a child suffering from serious vaccine side effects. As narrative events are more salient and thereby likely more easily retrievable from memory compared to non-narrative information, their probability (e.g., in terms of risk perceptions associated with the described event) will be overestimated when an availability heuristic is adopted.

Experiment 1 involved 418 participants from the United States (US) and United Kingdom (UK). It compares a narrative vaccination message with a non-narrative, expository message to test whether it evokes the availability heuristic and to explore whether it elicits other mechanisms (e.g., less resistance against the message) and outcomes (e.g., shifts in attitude certainty). Experiment 2 (n = 403 US and UK participants) was designed to further examine the exploratory findings from experiment 1, specifically aimed at examining a mediating role of cognitive resistance and a moderating role of prior vaccine hesitancy in the potentially persuasive effects of anti-vaccination narratives. (Cognitive resistance was measured with seven items, four on counter-arguing (e.g., "I found myself actively disagreeing with the author") and three on negative cognitions [i.e., "the thoughts I had about this message were unfavorable; positive (reversed); bad"].)

Four text versions were developed that discussed early childhood vaccination, using measles as an example. All versions were based on often-consulted sources on the internet (including official information from the vaccine-promoting website CDC.org and testimonials from the vaccine-critical website vaxtruth.org). The texts were relatively lengthy to increase the probability of participants experiencing narrative transportation and allowing differences between the texts to manifest. All texts contained general information about vaccines, as well as 12 elements describing measles symptoms and 12 elements describing vaccine side effects, each mentioned once. Content was manipulated by (i) replacing vaccine-positive arguments from the pro-vaccine condition (e.g., about herd immunity) with vaccine-critical arguments in the anti-vaccine condition (e.g., about natural immunity) and (ii) replacing the emphasis on measles symptoms in the pro-vaccine condition with an emphasis on vaccine side effects in the anti-vaccine condition. Format was manipulated by replacing factual contextual information from the expository text (e.g., describing the Center for Disease Control and Prevention (CDC)'s recommendations to follow the vaccination schedule) with personal contextual information to create a narrative text (e.g., describing how a mother weighed options regarding vaccination to choose, in her specific situation, what is best for her child).

Overall, the findings of the experiments show no empirical support for a role of the availability heuristic in response to vaccination information. That is, reading a narrative text about vaccination did not result in greater experienced ease of retrieval and increased risk perceptions than reading an expository text, even when taking the anti- vs. pro-vaccine content of the text into account. However, the availability heuristic "might still play a role in the process leading up to a vaccine decision in real life, but the part of the process that was highlighted in [experiment 1] found no evidence for such a role. Specifically, [the] findings suggest that the availability heuristic does not play a causal role in the short-term effects of processing information about vaccines."

The researchers note that, in experiment 1, exploratory analyses did indicate that an anti-vaccination narrative (vs. expository) might reduce cognitive resistance, decrease vaccination attitudes, and reduce attitude certainty, especially for those who were more vaccine hesitant. Experiment 2 formally tested this notion and showed that prior vaccine hesitancy, not narrative format, predicts cognitive resistance and post-reading attitudes. Hesitant participants showed less resistance toward an anti-vaccine text than vaccine-supporting participants, as well as less positive post-reading attitudes and attitude certainty.

These findings demonstrate that cognitive responses were outweighed by belief consistency processes, which affected both the way in which people processed information and their post-reading vaccine perceptions. This result stresses the necessity of taking prior knowledge, experiences, beliefs, and attitudes into account when formally studying the impact of communication on highly debated topics like vaccines. One implication is that stakeholders such as healthcare providers, communication specialists, and policymakers should not blindly trust in storytelling techniques as the solution for current (mis-)perceptions. However, combining this study's findings with earlier research "does suggest that vaccine risk communication in a narrative format might help reach affective objectives, especially when people with more experiences and stronger prior vaccine attitudes are exposed to more instances of narrative evidence."

In conclusion, the "findings show that a narrative format is not necessarily a more effective way to provide evidence-based information than the more frequently used expository format, as narrative impact is likely context-dependent and relies on many factors that should be further investigated."