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Incidental similarity

Author: Dr Simon Moss


Research indicates that people who share some trivial similarity, such as their birth date or initials, are more likely to trust and cooperative with one another. Similarly, individuals tend to like people with whom they share these similarities. Finally, they are more persuaded by someone with whom they share such similarities (e.g., Miller, Downs, & Prentice, 1998).

Empirical evidence

A variety of studies have confirmed that incidental similarities foster these positive consequences. In one study, Miller, Downs, and Prentice (1998) showed that individuals are more inclined to cooperate with each other, in the context of a Prisoner's dilemma, is they believed, albeit incorrectly, they shared the same birthday. Similarly, after individuals were told they share the same birth date as Rasputin, their perceptions of this historical figure were more lenient (Finch & Cialdini, 1989).

In addition to the same birth date, other similarities have also been shown to evoke these positive implications. As Burger, Messian, Patel, del Prado, and Anderson (2004) revealed, individuals are more likely to comply with the requests of someone with whom they believe they share the same first name or a similar fingerprint. In addition, Brendl, Chattopadhyay, Pelham, and Carvello (2005) demonstrated that individuals are more inclined to choose a brand that begins with the same letter as their first initial. Pelham, Mirrenberg, and Jones (2002) showed that people are more inclined to choose a job that begins with the same letter as these initials: People are more likely to choose to become a lawyer rather than dentist if their name is Laverne instead of Denise, for example.

Gueguen and Martin (2009) also showed that incidental similarity also increases the likelihood of mimicry. That is, according to Gueguen and Martin (2009), if individuals share some incidental or trivial similarity, they are more motivated to form a relationship with one another. Mimicry, in which individuals mirror the gestures and mannerisms of one another, such as rub their face at similar times, might represent a means to facilitate the formation of this rapport.

Effort and deliberation

Incidental similarity has also been shown to increase the level of effort or deliberation that individuals dedicate to some object or message. For example, as Howard and Kerin (2010) showed, individuals are more likely to scrutinize a resume carefully if they share the same name as the applicant. Similarly, they examine a brand more methodically and comprehensively that also shares their name. That is, individuals devote more effort to people, objects, or brands that, in some sense, are closely related to themselves.

Specifically, as Howard and Kerin (2010) demonstrated, individuals recall more information about people or brands with which they share a similar name. They dedicate more time to evaluating people with whom they share the same name. Nevertheless, they do not always form positive attitudes towards people or brands with which they share a similar name. Because they may scrutinize these people or brands more closely, they will form positive attitudes only if applicable--that is, only if these people or brands do demonstrate justifiable benefits.


Sense of connection

Several mechanisms are assumed to underpin this effect of incidental similarity. In particular, as Jiang, Hoegg, Dahl, and Chattopadhyay (2009) showed, when individuals share an incidental or trivial similarity, they experience a sense of social connection. This social connection, then, translates into trust, cooperation, and other positive consequences.

To assess this hypothesis, in one study, conducted by Jiang, Hoegg, Dahl, and Chattopadhyay (2009), university students were informed about a personal training program. They received information about the trainer, including past achievements and demographic details. Some participants discovered they shared the same birthday as this trainer. Next, this trainer presented a speech. Furthermore, participants answered questions about their attitudes towards this program, such as the extent to which this initiative seems helpful. Intentions to register with this program were also sought. Finally, the degree to which they felt connected to the personal trainer was assessed.

As hypothesized, if participants assumed they shared a birth date with this trainer, they were more inclined to like and register with this program. A sense of connection with this trainer mediated these relationships. Hence, incidental similarity seems to foster a sense of connection.

A subsequent study, also reported by Jiang, Hoegg, Dahl, and Chattopadhyay (2009), examined whether or not this effect of incidental similarity diminishes in individuals who are not as inclined to seek connections. Participants who endorsed questions like "I feel distant from people", and thus do not tend to seek a connection, were not as influenced by incidental similarity.

Another study, also conducted by Jiang, Hoegg, Dahl, and Chattopadhyay (2009), demonstrated that incidental similarity does not translate to positive consequences whenever the need to seek connections is satiated. That is, when individuals were exposed to words like accepted, involved, or included--priming a sense of connection--they were not more likely to be persuaded by someone with whom they share the same birth date. Their sense of connection has already been fulfilled. Thus, they were not as sensitive to other cues that indicate possible connections.

Implicit egotism and self enhancement

In contrast, Brendl, Chattopadhyay, Pelham, and Carvello (2005) maintain that individuals tend to form positive associations with themselves, called implicit egotism. This positive evaluation of themselves extends to personal details and characteristics as well. They will, therefore, tend to perceive personal cues, like their initials, favorably. Hence, other people who correspond to these cues are also perceived favorably.

Brendl, Chattopadhyay, Pelham, and Carvello (2005) did uncover some evidence that implicit egotism is relevant to this effect of incidental similarity. In particular, self affirmation, in which individuals contemplate their strengths, tends to curb the benefits of this incidental similarity. Self affirmation, in contrast to a sense of threat, reduces the inclination of individuals to inflate their perception of themselves and thus diminishes implicit egotism.

Jiang, Hoegg, Dahl, and Chattopadhyay (2009) attempted to ascertain the contexts in which a sense of connection or implicit egotism underpins the effects of incidental similarity. They showed that a sense of connection is the primary mechanism in most interpersonal contexts. That is, in these contexts, the need to feel connected is especially pronounced. In contrast, implicit egotism is the primary mechanisms in other contexts, when individuals evaluate objects instead of people. Specifically, the effect of incidental similarity on evaluations of a dentist were mediated by social connections& the effect of incidental similarity on evaluations of a clinic were probably mediated by implicit egotism& that is, these effects were curbed by self affirmation.

Factors that moderate the impact of incidental similarity

Several factors moderate the benefits of incidental similarity. For example, if individuals do not like someone else, incidental similarities with this person do not translate into trust and cooperation. Indeed, in this context, similarities can decrease, rather than increase, the likelihood of these consequences (e.g., Miller, Downs, & Prentice, 1998). As Jiang, Hoegg, Dahl, and Chattopadhyay (2009) showed, this effect is especially pronounced if individuals believe they may encounter this person again in the future.


Brendl, C. M., Chattopadhyay, A., Pelham, B. W., & Carvallo, M. (2005). Name letter branding: valence transfers when product specific needs are active. Journal of Consumer Research, 32, 405-15.

Burger, J. M., Messian, N., Patel, S., del Prado, A., & Anderson, C. (2004). What a coincidence! The effects of incidental similarity on compliance. Personality and Social Psychology Bulletin, 30, 35-43.

Finch, J. F., & Cialdini, R. B. (1989). Another indirect tactic of (self-) image management: boosting. Personality and Social Psychology Bulletin, 15, 222-32.

Gueguen, N., & Martin, A. (2009). Incidental similarity facilitates behavioral mimicry. Social Psychology, 40, 88-92.

Howard, D. J., & Kerin, R. A. (2010). The effects of name similarity on message processing and persuasion. Journal of Experimental Social Psychology, 47, 63-71.

Jiang, L., Hoegg, J., Dahl, D. W., & Chattopadhyay, A. (2009). The persuasive role of incidental similarity on attitudes and purchase intentions in a sales context. Journal of Consumer Research, 36, 778-791.

Miller, D. T., Downs, J. S., & Prentice, D. A. (1998). Minimal conditions for the creation of a unit relationship: The social bond between birthdaymates. European Journal of Social Psychology, 28, 475-81.

Pelham, B. W., Mirrenberg, M. C., & Jones, J. T. (2002). Why Susie sells seashells by the seashore: Implicit egotism and major life decisions. Journal of Personality and Social Psychology, 82, 469-487.

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Last Update: 7/17/2016