Abnormality (Clinical Psychology) A2, Edexcel



  • Defining a behaviour/person as abnormal implies something undesirable and requiring change.
  • Psychologists need methods for distinguishing 'normal' from 'abnormal'.
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Statistical Definition of Abnormality

  • A person's trait, thinking or behaviour is classified as abnormal if it is rare or statistically unusual.
  • Necessary to be clear about how rare a trait or behaviour needs to be before we class it as abnormal.
  • Any human characteristic is spread in a normal way across the general population.
  • When plotted on a graph, it will form a normal distribution curve.
  • The majority of people will fall in the middle of the graph with the minority being at either extreme end of the graph.
  • The same is true of normal and abnormal behaviour.
  • If someone's behaviour falls in the top or bottom 2.5% then it is considered to be abnormal.
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Statistical Definition Continued...

  • EXAMPLE - Average IQ in the population is 100.
  • The further from 100 you look, the fewer people you find.
  • If IQ falls in the bottom or top 2.5% then it is to be considered abnormal.
  • EXAMPLE - 65% of the population have an IQ between 85 and 115
  • So if the majority (95%) of the population have an IQ of between 70 and 130, those that fall out of this are considered abnormal.
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Evaluating Statistical Definition

STRENGTH - It is an objective definition, therefore one that all clinicians can use to ensure consistency in diagnosis.

WEAKNESS - Does not give a clear-cut definition and takes away the subjectivity of clinicians diagnosis.

WEAKNESS - Doesn't take account of cultural variations.

WEAKNESS - If a person's score is only one or two above what is classed as abnormal, they may not get the help that they need.

WEAKNESS - Some behaviours that people show everyday such as anxiety may be considered normal but abnormal in a clinical sense.

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Deviation From Social Norms

  • Another definition of abnormality.
  • Every society has accepted standards of behaviour, these are sometimes written as part of the law.
  • Others are implicit: they are generally accepted but not legally binding.
  • Social norms allow for the regulation of normal behaviour.
  • One approach to defining abnomality is to consider deviations from social norms as an indicator of abnormal behaviour.
  • A person's thinking or behaviour is classed as abnormal if it violates the rules about what is expected or acceptable behaviour in a particular social group.
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Deviation From Social Norms Continued...

  • Their behaviour may be incomprehensible to others or make others feel threatened or uncomfortable.
  • To define people's mental health in terms of deviation from social norms suggests that those who behave in a socially deviant or incomprehensible way should be regarded as abnormal because they break with conventions and so not do what is normally expected.
  • Some roles in society also come with what is considered to be normal behaviour, such as doctors are expected to be caring towards their patients.
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Evaluation Of Deviation From Social Norms

WEAKNESS - Can lead to an abuse of a person's rights based on what society sees as normal.

WEAKNESS - It is culturally biased. What is unacceptable in one culture may be seen as acceptable in another culture.

STRENGTH - At times, breaking with the dominant culture is something to be applauded (freedom fighters)

STRENGTH - Allows us to consider different behaviour which may not on their own be classified as abnormal.

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