Our goal was to explore how beliefs about categories influence interactions with members of those categories within the mental health domain. We specifically explored beliefs related to attaining category membership (contagion and causal origin), as well as beliefs related to a category’s underlying nature (causal essentialism and controllability of the category’s symptoms). In two experiments, we showed that category beliefs could moderate interactions with category members, with contagion beliefs showing special importance. We found that in real disorders, three predictors related to attaining category membership (contagion, psychological origin, environmental origin) and one predictor related to the nature of the category (all-or-none membership) predicted willingness to interact with category members. When we isolated these variables from their real-world interconnections by testing artificial disorders, only communicability influenced interaction-willingness judgments.

Although Experiment 2 demonstrated the importance of communicability beliefs when isolated from other factors, beliefs can never be presented in such isolation in the real world. For example, knowing that something has wings and is a bird almost obligatorily results in believing it also has feathers and could fly. In mental disorder categories, thinking a disorder is contagious could similarly be connected to other beliefs. For example, believing a disorder is communicable may prime a person to think about the environmental sources it can be contracted from or the psychological traits another person could display that may influence one’s own behavior. In turn, thinking a disorder has all-or-none membership may be detrimental in disorders believed to be contagious, because one would contract the full disorder as opposed to a partial form of the condition. In real categories, people may feel justified to make these deductions from one belief to the next. With the sparse information in Experiment 2, these deductions may not have been justified (for similar ideas of information justifying belief application, see Marsh & Ahn, 2009; Yzerbyt, Schadron, Leyens, & Rocher, 1994). Future research should explore how contagion beliefs are interconnected to other beliefs about mental disorder categories.

One element of these findings deserves special notice: People were willing to endorse mental disorders as communicable. What underlies this idea that mental disorders are contagious? There is evidence in the mental health literature for the transmission of mental disorder symptoms; symptoms of specific mental disorders have been shown to spread among peers (e.g., binge eating: Crandall, 1988; childhood depression: Dishion & Piehler, 2009; van Zalk, Kerr, Branje, Stattin, & Meeus, 2010). Laypeople believing that mental disorders are communicable may reflect a sophisticated understanding of how mental disorder symptoms move through social networks. Alternatively, endorsing mental disorder communicability may reflect a much less sophisticated set of contagion beliefs that represent something similar to a disgust response (Rozin et al., 1986). It is an empirical question for future research to address what exactly is the underlying origin of these communicability beliefs.

Participants in Experiment 3 rarely provided specific descriptions of how mental disorder contagion happens. Instead, participants often provided general social descriptions such as “The person’s anxiety will rub off” for generalized anxiety disorder, or for alcohol abuse, “If you hang out with someone that drinks all the time you will soon be drinking a lot as well.” Two things are instructive from the nonspecificity of these descriptions. One, the cited social-transmission mechanisms often highlighted acquiring a single trait from another person. From a categorization point of view, there is a large difference between exhibiting a single feature of a category and being a category member. Laypeople might not perceive this difference in the domain of mental health. Instead, mental disorder category membership may be seen as a “slippery slope,” where emulating dysfunctional behavior is the first step toward being a member of a disorder category. This insinuates a very different process of category membership attainment than for everyday categories, such as birds or apples. Examining the idea of acquiring disorder category membership from another person can help illuminate the issue of what it means to be a member of a disorder category and, more generally, shed light on how people view category membership as being obtained.

Second, the lack of specific knowledge about how mental disorders are “caught” may be integral to why people do not want to interact with members of communicable disorder categories. For example, if a friend has the flu, you know not to share a drinking glass with her. However, if the same friend has major depression, how would you protect yourself against transmission? More generally, when a category’s causal origin is not well understood, people may be more likely to think membership can be acquired. For example, if a person is unsure what makes something a piece of art, she may think a painting could, over time, become categorized as art if hung in a gallery near other pieces of art; someone who has a strict idea of what makes something art may deem this art-by-proximity mechanism implausible. Future research could investigate whether the concreteness of causal origin beliefs moderates beliefs about acquiring category membership.

Our results present interesting counterpoints to existing literature. We do not replicate findings that suggest essentialism is tied to unwillingness to interact with mental disorder category members (Haslam, 2011). We believe this is in part because we tested a more general form of essentialism, as opposed to a strictly genetic form. It is not necessary that an essence take a biological form (see Gelman & Hirschfeld, 1999). For example, tool categories can be endorsed as possessing essences (Ahn et al., 2013). As such, believing that a category has a genetic essence underlying a category is a much more specific belief than generally endorsing that there is some form of causal essence that defines category membership. Although our findings suggest that belief in a general causal essence does not predict interaction willingness, belief in a specific genetic factor may still predict such interactions. In a similar vein, we did not find that a biological causal origin moderated willingness to interact with members of disorder categories. Again, we did not ask about genetic biological factors specifically, but rather about biological factors more generally. Beliefs in genetic causes may predict interaction willingness even if more general biological factors do not. Future research can explore the role genetic explanations play alongside contagion in predicting interaction with mental disorder category members.

Our experiments specifically investigated the domain of mental health. How would our findings apply to other categories to describe how people’s beliefs influence willingness to interact with category members? Specifically, would contagion beliefs be influential in domains outside of health? We demonstrated that people endorse the contraction of a mental health illness through close physical contact, fitting a larger literature demonstrating that people hold what can be seen as implausible or irrational beliefs about the nature of contagion (Buck et al., 2013; Rozin & Nemeroff, 2002). This could mean that just because another domain does not on its surface seem to involve contagion, people may still act like characteristics of those categories are transmissible. Presumably, mental disorders are not communicable, and yet people still endorse disorder contagion. The social element of reported transmission mechanisms suggests that interactions with any human social category (e.g., race, sexual orientation) could be guided by whether category features or membership itself is believed to be transmittable between people (see, e.g., Cameron & Cameron, 1996).

More generally, we believe that the importance of contagion in the mental health domain may reflect a more general focus on how things become members of a category. In mental health, this is thinking about whether the person may have caught the disorder from someone else or could transmit that membership. In other domains, this may be thinking about whether the instance became a member of the category in a way that is natural for that domain. For example, a voter may think about what makes a politician a valid representative of her state (e.g.: Was this person born here or did she just set up legal residence to run for office?) or a shopper may wonder if a piece of fruit was naturally a fruit or if it was genetically modified to be this type of fruit. How the fruit or politician in question came to become a member of their respective category may influence decision making about interactions with the category member. People’s consumer preferences are very sensitive to how something becomes what it is claimed to be. People will pay far less money for exact copies of original masterworks of art not created by the original artist (Newman & Bloom, 2012). Lab-produced diamonds that are chemically identical to natural diamonds command a much lower price than do mined diamonds (Scott & Yelowitz, 2010). People show a strong prejudice against genetically modified or lab-engineered food (Rozin et al., 2004; Tenbült, de Vries, Dreezens, & Martijn, 2005). These preferences suggest that becoming a category member through an unnatural route results in people being unwilling to interact with the member, compared with its (even sometimes identical) counterparts that are seen to have attained membership in more domain-appropriate ways. Future research could explore how contagion beliefs are related to believing something becomes a category member through “natural” ways.

Our research informs an important missing element in the categorization field of how knowledge is translated into action. These findings tell us specifically about category beliefs that guide interactions with members of mental disorder categories. More generally, we believe our results shed light on how the knowledge people have stored about categories translates to guiding actual interactions with category members. Moving research in this direction can help us more fully understand how category knowledge influences behavior in real-world settings.