Statistical infrequency

• How does statistical infrequency define abnormality?

  abnormality is defined as behaviours or characteristics that are rare or unusual in relation to the wider population
• when would we use the statistical approach?

  when we are dealing with characteristics or behaviour that can be reliably measured
• example of a characteristic that can be reliably measured

  intelligence
• normal distribution


  in any human characteristic, the majority of people's scores will cluster around the average, and that the further we go above or below that average, the fewer people will attain that score
• what is the average IQ set at?

  100
• in a normal distribution how many people will have a score between 85 and 115, in the case of IQ?

  68%
• what is the range for normal distribution for IQ?

  85 to 115
• how many people have a score below 70?

  2%
• what are those scoring below 70 considered?

  unusual or abnormal and are liable to receive the diagnosis of a psychological disorder - intellectual disability disorder
• what disorder do those scoring below 70 in IQ have?

  intellectual disability disorder
• strength - statistical infrequency is highly useful

  - statistical infrequency is used in clinical practice, both as part of formal diagnosis and as a way to assess the severity of an individual's symptoms

  
  

  - for example, a diagnosis of intellectual disability disorder requires an IQ of below 70

  
  

  - an example of statistical infrequency used in an assessment tool is the Beck depression inventory - a score of 30+ is widely interpreted as indicating severe depression

  
  

  this shows that the value of the statistical infrequency criterion is useful in diagnostic and assessment processes, therefore it has real world application
• limitation - infrequent/unusual characteristics aren't always negative, they can be positive as well

  - for every person with an IQ below 70 there is another with an IQ above 130

  
  

  - we would not think of someone as abnormal for having a high IQ, therefore those with negative unusual characteristics, are considered abnormal

  
  

  - similarly, we would not consider someone having a very low depression score on the BDI as abnormal

  
  

  - these examples show that being unusual or at one end of a psychological spectrum does not necessarily make someone abnormal

  
  

  this means that, although statistical infrequency can form part of assessment and diagnostic procedures, it is never sufficient as the sole basis for defining abnormality