The power of the in-group: Similarity and compliance

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But why is it that this type of advertising is effective?

The presence of groups is the underlying basis for much of our social cognition, and indeed it has been suggested that groups play such an important role in our processing that this may be the reason for the relatively large size of the neocortex in humans – to allow for the maintenance of more social relationships (Dunbar, 1992).

If groups play such an important role in our social processing, we can expect their presence to have some visible effect on human behaviour.

A key aspect which ties members of an in-group together is similarity: people who are similar to one another will consider themselves as part of an in-group. Burger, Messian, Patel, Prado and Anderson (2004) investigated the relationship between perceived similarity and compliance to a request:

They first demonstrated the effect that even relatively meaningless similarities can have, showing an increased compliance to a request if the person asking and the person receiving the request shared the same first name. This is an effect known as the minimal group paradigm, something which truly emphasises the power of the in-group as the nature of the group does not have to be important – even trivial similarities can cause an in-group bias which can lead to increased compliance.

Figure 1 shows the percentage of participants who complied to a request when they either did or did not share the same first name as the confederate

As well as demonstrating an in-group bias for trivial similarities, Burger et al (2004) showed an even stronger effect on compliance when the similarity is uncommon – something similar between two people that not many other people share. In the study, participants were in one of three conditions: a control condition, a common similarity condition – in which they were told they shared a fingerprint type with the confederate, that around 80% of the population had – or the uncommon similarity condition – in which the fingerprint type they supposedly shared was only present in 2% of the population.

Figure 2 shows the percentage of participant's who complied to a request in each of the experimental conditions

In both experiments, the request made was for the participant to read an eight-page essay and provide a page of written feedback – not exactly a small ask! Therefore, the compliance rates seen in some of the similarity conditions – 82% for an uncommon similarity – shows the robustness of the effect, and the role that similarity and in-group bias plays in our everyday decision making.

So, next time you want your colleague to cover a shift, make sure you first illustrate some common ground between the two of you – especially if you can think of some unique similarities – in order to enforce a real sense of an in-group!

References:
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(1), 35-43.

Dunbar, R. I. (1992). Neocortex size as a constraint on group size in primates. Journal of Human Evolution, 22(6), 469-493.