Spock's Not One of Us! Exploring the In-Group Overexclusion Effect

Liberal or Conservative?

We all belong to many different social groups. For example, we belong to groups based on our age, gender, nationality, sexuality, and occupation, to name just a few. Most of the time, it's fairly easy to work out who belongs to which group. But sometimes it's not that clear. For example, if you had to guess, would you say that the man opposite is a liberal or a conservative? Well, social psychologists have found that your answer will sometimes depend on which group you belong to. If you're a liberal, then you'll probably guess that the man is a conservative. And if you're a conservative, then you'll probably guess that he's a liberal. This mysterious phenomenon is called the in-group overexclusion effect. 

Human or Vulcan?

Now sit up straight - it's formal definition time: The in-group overexclusion effect is an intergroup effect in which people are more likely to classify ambiguous individuals as members of the out-group (i.e., the group that they don't belong to) than their in-group (i.e., the group that they do belong to). So, to take a slightly less real world example, you’d be more likely to classify the lovely Mr Spock as a Vulcan (i.e., an out-group member) rather than a human (i.e., an in-group member), even though he is half human and half Vulcan. (Apologies if you’re of the Vulcan persuasion by the way. My example only works if you're human!)

Based on social identity theory (Tajfel and Turner, 1979), Leyens and Yzerbyt (1992) proposed a motivational explanation for the in-group overexclusion effect: People are motivated to protect their in-group from intrusion (contamination, pollution!) by negatively-valued out-group members in order to protect the positivity of their associated social identity and self-esteem. If those no-good out-group members get classified as in-group members, then they'll sully your group with their negativity and, since part of your self-esteem is derived from belonging to a positive in-group, you're motivated to err on the side of caution and make sure that you exclude anyone from your group who shows even a hint of being an out-group member.

There's some good evidence in support of the social identity part of this explanation: People who identify strongly with their in-group are more likely than those who identify weakly to show the overexclusion effect (Castano, Yzerbyt, Bourguignon, and Seron, 2002). However, to date, there has been no direct evidence for the motivational part of the explanation - the part that relates to the in-group's positivity and your own self-esteem. Do people excluded ambiguous others from their group in order to protect the their group's positivity and their own self-esteem? My colleague, Dr Stefania Paolini, and I aimed to test this motivational part. We made two predictions:

Prediction 1: If the overexclusion effect is caused by the need to protect the in-group’s positivity, then it should only occur when the in-group is positive and the out-group is negative (and not vice versa) because it is only in this situation that group members would be motivated to exclude nasty negative out-group members from their nice positive in-group.

Prediction 2: If the overexclusion effect is caused by the need for self-esteem, then people who have low self-esteem should be most likely to display the effect because they have the greatest need for self-esteem.

To test these predictions, we asked 122 undergraduate students to complete Rosenberg’s (1965) Self-Esteem Scale. This scale includes 10 statements such as "I feel that I have a number of good qualities." Respondents are asked to indicate how much they agree or disagree with each statement.

Next, participants completed a memory recall task in which they were presented with a series of diagrams on a computer screen like the one below. Each diagram showed two groups of people, with each person represented by a code number from 1 to 20. One group was located inside a picture of a bucket of soapy water. The other group was located inside a picture of a dustbin full of rubbish. We asked participants to consider the people in the bucket as "clean" and people in the dustbin as "dirty." So, obviously, the clean group was a positive group and the dirty group was a negative group.

Participants were given an identity number (3 or 14) which they were told identified them, and this code number appeared in one of the two groups. So, one of the groups represented an in-group, and the other represented an out-group. In the diagram above, the dirty group is the in-group because it contains the numbers 3 and 14 (the participants' identity numbers), and the clean group is the out-group. But in other diagrams that we presented, the clean bucket contained the in-group members and the dirty dustbin contained the out-group members.

For each diagram that they viewed, participants were given 5 seconds to memorize which people belonged to which group. The diagram was then removed, a person’s code number was presented, and participants were asked to recall which group the person had belonged to, like this: “Person Number 7. Clean or Dirty?” Our predictions related to those instances in which participants made errors in the memory recall task and assigned a person to the wrong group.

Consistent with previous research, participants erred on the side of caution and misassigned more in-group members to the out-group than they misassigned out-group members to the in-group. In other words, they showed the classic in-group overexclusion effect. However, consistent with Prediction 1, this effect was qualified by whether the group was clean or dirty. The overexclusion effect only occurred when the in-group was clean (i.e., positive) and the out-group was dirty (i.e., negative) – the red line in the diagram below. There was no significant overexclusion effect when the in-group was dirty and the out-group was clean – the green line in the diagram. Hence, consistent with Prediction 1, the overexclusion effect only occurred when the in-group was positive and out-group was negative and not vice versa.

To test Prediction 2, we computed an index that represented the overexclusion effect by subtracting the number of misassignments to the in-group from the number of misassignments to the out-group. Larger positive scores on this index indicated a larger overexclusion effect. Consistent with Prediction 2, participants' scores on the Rosenberg Self-Esteem Scale negatively predicted the overexclusion effect. Hence, the lower people’s self-esteem, and the greater their need for self-esteem, and the more likely they were to show the overexclusion effect by misassigning people to the out-group rather than the in-group.

Our results provide an important piece in the puzzle of the in-group overexclusion effect - the motivational piece. They tell is that it's not enough to simply identify with your group to show the overexclusion effect - you also have to value your group positively. Admittedly, identification and in-group favouritism often go hand in hand, but there are some cases where they diverge. For example, members of stigmatized, low status, and minority groups might identify with their group but also recognise its inherent negativity.

Interestingly, our research also suggests that people with low self-esteem are the most likely to exclude people from their group. Transporting back to the USS Enterpise, perhaps Dr McCoy ("Bones") had low self-esteem because, as Spock observed, he was always the first to exclude Spock from the human race:

Dr McCoy: “Are you out of your Vulcan mind? No human can tolerate the radiation that's in there!”

Mr Spock: “As you are so fond of observing, doctor, I am not human!”

Star Trek II: The Wrath of Khan (1982)

For further information, please see the following journal article:

Rubin, M., & Paolini, S. (2014). Out-group flies in the in-group’s ointment: Evidence of the motivational underpinnings of the in-group overexclusion effect. Social Psychology DOI: 10.1027/1864-9335/a000171

For a self-archived version of this article, please see here.