How Heuristics and Cognitive Biases Affect Vaccination Decisions

"...knowledge of how people make decisions can better inform strategies that encourage health-behavior change..."

Under-vaccination can be traced to multiple causes (the "5As"): access, affordability, awareness, acceptance, and activation. This paper focuses on acceptance, with a look at factors pertaining to individual or parental compliance - specifically, the psychology of judgment and decision making. It explores how heuristics and cognitive biases affect vaccination decision making, when and how social processes play a role, and how attitudes towards vaccines might reflect a more general underlying attitude or ideology. The purpose of the analysis is to help inform more appropriate public health interventions.

As explained here, a heuristic is a mental shortcut that allows people to solve problems and make judgments quickly and intuitively. Though helpful in many situations, heuristics can lead to biases (or systematic errors) when making predictions. For example:

• "Affect heuristics" emerge when narratives provide information on an individual's experience that may evoke an emotional response (affect) guiding risk judgment beyond objective information. The internet is increasingly becoming the source of health-related information narratives containing personal information of unknown validity. One study cited here found that the number of narratives, as opposed to objective statistical information, was the critical variable influencing the judgments made about the risk of adverse events following vaccination and thus decreasing vaccination intentions.
• The "availability heuristic" is a mental shortcut that relies on immediate examples that come to mind when evaluating how risky an outcome is. That is, individuals rate a hazard as riskier when it has a more memorable but less probable outcome than a hazard with a less memorable but more probable outcome. Relatedly, people may overestimate the probability of diseases that have increased case-fatality rates without considering incidence.
• "Ambiguity aversion" is the displayed preference for known or certain probabilities over unknown or uncertain probabilities.
• "Optimism bias" relates to our inferences about the probability of future events and is marked by an overestimation of the probability of positive things or an underestimation of the probability of negative things happening to oneself.
• "Anticipated regret" (or regret aversion) involves individuals anticipating regret of a particular outcome from vaccinating or not vaccinating.
• "Omission bias" is the tendency to prefer harm due to an act of omission over an act of commission. This bias was suggested to play a role in a study that found that parents were willing to accept significantly worse outcomes from influenza disease than from its vaccine.
• "Confirmation bias" could be seen in a study in which parents preferred the headers of messages that were consistent with their beliefs and rated the information that was consistent with their belief as more credible and useful.
• The "framing effect" is a cognitive bias where choices are influenced by how message content is presented (e.g., in a gain- vs. loss-frame).
• The "Dunning-Krueger effect" happens when people wrongly overestimate their knowledge or ability in a specific area, such as by believing they know more than medical doctors about the causes of autism, which one study found was correlated with endorsement of "anti-vaccination" policies.

Work generated within the field of Moral Foundation Theory suggests that heuristics and cognitive biases can be understood as having underlying roots in moral judgment. An Australian study found that rejectors of vaccines more strongly endorsed the moral domains of purity and economic and lifestyle liberty. Another theory proposes that the drivers of anti-vaccination attitudes are "attitude roots", meaning that individuals have emotional or intuitive attitudes towards vaccines (e.g., conspiratorial beliefs) that motivate them to search for and accept/reject evidence according to how well it supports their previous attitudes.

In conclusion: "If we understand our cognitive limitations, our heuristics and their consequent biases, and how our beliefs and attitudes towards vaccines might be influenced by emotions, moral foundations or group alignments, we can better devise means of working around these to achieve our common goals."

Click here for the article in Portuguese (10 pages, PDF).