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In this section, we'll define the primary building blocks of the metrics we'll use to evaluate classification models. But first, a fable: An Aesop's Fable: The Boy Who Cried Wolf (compressed) A shepherd boy gets bored tending the town's flock. To have some fun, he cries out, "Wolf!" even though no wolf is in sight. The villagers run to protect the flock, but then get really mad when they realize the boy was playing a joke on
them. [Iterate previous paragraph N times.] One night, the shepherd boy sees a real wolf approaching the flock and calls out, "Wolf!" The villagers refuse to be fooled again and stay in their houses. The hungry wolf turns the flock into lamb chops. The town goes hungry. Panic ensues. Let's make the following definitions: We can
summarize our "wolf-prediction" model using a 2x2 confusion matrix that depicts all four possible outcomes:
True Positive (TP):
| False Positive (FP):
|
False Negative (FN):
| True Negative (TN):
|
A true positive is an outcome where the model correctly predicts the positive class. Similarly, a true negative is an outcome where the model correctly predicts the negative class.
A false positive is an outcome where the model incorrectly predicts the positive class. And a false negative is an outcome where the model incorrectly predicts the negative class.
In the following sections, we'll look at how to evaluate classification models using metrics derived from these four outcomes.
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Last updated 2022-07-18 UTC.
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social identity theory, in social psychology, the study of the interplay between personal and social identities. Social identity theory aims to specify and predict the circumstances under which individuals think of themselves as individuals or as
group members. The theory also considers the consequences of personal and social identities for individual perceptions and group behaviour. Social identity theory developed from a
series of studies, frequently called minimal-group studies, conducted by the British social psychologist Henri Tajfel and his colleagues in the early 1970s. Participants were assigned to groups that were designed to be as arbitrary and meaningless as possible. Nevertheless, when people were asked to assign points to other research participants, they systematically awarded more points to
in-group members than to out-group members.History
The minimal-group studies were interpreted as showing that the mere act of categorizing individuals into groups can be sufficient to make them think of themselves and others in terms of group membership instead of as separate individuals. That finding deviated from a common view at the time, namely, that an objective conflict of interest is a central factor in the emergence of intergroup conflict.
Thus, social identity theory originated from the conviction that group membership can help people to instill meaning in social situations. Group membership helps people to define who they are and to determine how they relate to others. Social identity theory was developed as an integrative theory, as it aimed to connect cognitive processes and behavioral motivation. Initially, its main focus was on intergroup conflict and intergroup relations more broadly. For that reason, the theory was originally referred to as the social identity theory of intergroup relations.
Later elaborations by Tajfel’s student John Turner and his colleagues on the cognitive factors relevant to social identification further specified how people interpret their own position in different social contexts and how that affects their perceptions of others (e.g., stereotyping), as well as their own behaviour in groups (e.g., social influence). Those elaborations constitute self-categorization theory, or the social identity theory of the group. Together, self-categorization theory and social identity theory can be referred to as the social identity approach.
Cognitive processes
Social identity theory was developed to explain how individuals create and define their place in society. According to the theory, three psychological processes are central in that regard: social categorization, social comparison, and social identification.
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Social categorization refers to the tendency of people to perceive themselves and others in terms of particular social categories—that is, as relatively interchangeable group members instead of as separate and unique individuals. For example, one can think of a certain person, Jane, as a feminist, a lawyer, or a football fan.
Social comparison is the process by which people determine the relative value or social standing of a particular group and its members. For instance, schoolteachers may be seen as having higher social standing than garbage collectors. Compared with university professors, however, schoolteachers can be seen as having lower social standing.
Social identification reflects the notion that people generally do not perceive social situations as detached observers. Instead, their own sense of who they are and how they relate to others is typically implicated in the way they view other individuals and groups around them.
Someone’s social identity is then seen as the outcome of those three processes (social categorization, social comparison, and social identification). Social identity can be defined as an individual’s knowledge of belonging to certain social groups, together with some emotional and valuational significance of that group membership. Thus, while one’s personal identity refers to self-knowledge associated with unique individual attributes, people’s social identity indicates who they are in terms of the groups to which they belong.
Motivation
According to social identity theory, social behaviour is determined by the character and motivations of the person as an individual (interpersonal behaviour) as well as by the person’s group membership (i.e., intergroup behaviour).
People generally prefer to maintain a positive image of the groups to which they belong. As a result of social identity processes, people are inclined to seek out positively valued traits, attitudes, and behaviours that can be seen as characteristic of their in-groups.
That inclination may also cause them to focus on less favourable characteristics of out-groups or to downplay the importance of positive out-group characteristics. The tendency to favour one’s in-groups over relevant out-groups can affect the distribution of material resources or outcomes between in-group and out-group members, the evaluation of in-group versus out-group products, assessments of in-group versus out-group performance and achievement, and communications about the behaviour of in-group versus out-group members.
Strategies for status improvement
The motivation to establish a positive social identity is thought to lie at the root of intergroup conflict, as members of disadvantaged groups strive for improvement of their group’s position and social standing and members of advantaged groups aim to protect and maintain their privileged position.
According to the individual-mobility belief system, individuals are free agents who are capable of moving from one group to another. The defining feature of the system is the notion that group boundaries are permeable, such that individuals are not bound or restricted by their group memberships in pursuing position improvement. Thus, individuals’ opportunities and outcomes are viewed as dependent on their talents, life choices, and achievements rather than on their ethnic origin or social groups.
A very different belief system, known as the social change belief system, holds that changes in social relations depend on groups modifying their positions relative to each other. Status security depends on the perceived stability and legitimacy of existing status differences between groups. Stability and legitimacy tend to mutually influence each other: when positions are subject to change, existing intergroup differences in status appear less legitimate. Conversely, when the legitimacy of existing status differences between groups is questioned, the perceived stability of such relations is likely to be undermined.
The two belief systems, in turn, determine what people are most likely to do when they pursue a more positive social identity. Social identity theory distinguishes between three types of strategies for status improvement: individual mobility, social competition, and social creativity.
Individual mobility allows people to pursue individual position improvement irrespective of the group. It can also be an individual-level solution for overcoming group devaluation.
Social competition is a group-level strategy that requires group members to draw together and combine forces to help each other improve their joint performance or outcomes.
Finally, social creativity implies that people modify their perceptions of the in-group’s standing. That can be achieved by introducing alternative dimensions of comparison in order to emphasize ways in which the in-group is positively distinct from relevant out-groups. A second possibility is to reevaluate existing group characteristics to enhance in-group perceptions. A third possibility is to compare one’s group with another reference group in order to make the current standing of the in-group appear more positive.
Social creativity strategies are generally characterized as cognitive strategies because they alter people’s perceptions of their group’s current standing instead of altering objective outcomes. Nevertheless, it has been demonstrated that these strategies can constitute a first step toward the achievement of social change. Because social creativity strategies help preserve identification with and positive regard for the in-group, even when it has low status, over time those strategies can empower group members to seek actual position improvement for their group