Tania Lombrozo, Ph.D., is an Associate Professor in the Department of Psychology at the University of California, Berkeley. Her work explores several topics within the field of cognitive psychology, including how we seek and evaluate explanations and how we assess probability. Recently Dr. Lombrozo has studied a phenomenon called "omission bias," or the unconscious preference for not acting over taking action, as it relates to parents' decisions about vaccinating their children. This is particularly timely given the recent measles outbreak that stemmed in large part from unvaccinated individuals.
The following are Dr. Lombrozo's responses to questions posed by John Swartzberg, M.D., chair of the Berkeley Wellness editorial board, and Cecilie Bisgaard-Frantzen, a graduate student in public health at UC Berkeley.
What do you think is the reason for omission bias in parents who choose not to vaccinate their kids?
People definitely vary in the extent to which they exhibit omission bias, but not much is known about why some people exhibit it more than others. There is some evidence that people are more likely to exhibit omission bias if they tend to make decisions more intuitively, by going with their immediate feeling or gut reaction, rather than engaging in explicit, deliberate reflection. We also know a bit about the conditions under which people are more likely to exhibit omission bias. For example, people may be more likely to exhibit omission bias when making moral decisions than other types of decisions, and especially when the moral issue involves what’s called a “sacred” or “protected” value: an entity that we consider so valuable that we hate to even think about assigning a monetary value to it, or trading it off against other goods. Children’s wellbeing is likely a value of this type for most parents, which could make omission bias more pronounced for vaccination decisions than it is for other decisions.
How conscious do you think people are about omission bias?
I doubt people are conscious of omission bias. Like many psychological processes, the processes responsible for omission bias likely operate without our awareness. We may intuitively experience an option as more or less attractive than another, or imagine a counterfactual or hypothetical situation as more or less aversive than another, without recognizing exactly why we have the reactions we do.
It seems a current in our society is to question authority. How much of a role do you think that plays in a parent’s negative attitude toward vaccination?
I think this is one factor in some people’s decisions, but it’s important to be clear about which authority parents are questioning. People who do not vaccinate often belong to communities that do not vaccinate. Individual parents may be questioning the authority of science or of their doctor, but accepting the authority of a religious doctrine, of a particular parenting philosophy, or of other members of their community.
In addition to omission bias, what other psychological mechanisms do you think play a role in causing parents either not to immunize their children or to be hesitant about vaccination?
A variety of factors play a role. Some of them have to do with the persistence of misinformation: people often have inaccurate beliefs about the actual risks and benefits of vaccination, and psychological research suggests that simply presenting them with accurate information is rarely enough to make them reject those beliefs. Other factors are more social in nature: they have to do with the community that people belong to and how different decisions are valued within that community. One factor that’s received only a little attention, but that I suspect plays a role in many personal and policy decisions, is a preference for what people consider to be “natural.” This could manifest as hesitation to intervene on a “natural” process when it comes to vaccination decisions, and also in many other issues, like attitudes towards genetically modified foods.
What are your ideas of how individuals can guard against omission bias?
One suggestion is to be very explicit about your decision-making process. Write out the costs and benefits of each option, and think about how you’d weigh each possible outcome, without focusing on how each outcome is brought about (i.e., by an act versus an omission). Another suggestion is to try out some thought experiments. Instead of approaching a decision in a single way, try thinking about it in different ways. For instance, would you feel differently about your options if you swapped which outcome was associated with the act and which with the omission? Would you feel differently if the norm in your community were one decision, versus the other? These mental exercises can sometimes clarify why you’re attracted or repelled by a given option, and whether that reaction is really tracking what matters most in this case: what’s best for your child and your community.