STATISTICAL INFREQUENCY (SI)

• Defining abnormality in terms of statistics 


  The most obvious way to define anything as ‘normal’ or ‘abnormal’ is in terms of the number of times it is observed. 

  Statistics is about analysing numbers. 
• Behaviour that is rarely seen is abnormal 


  Any relatively ‘usual’ or often seen, behaviour can be thought of as ‘normal’.

  Any behaviour that is different, or rare, is ‘abnormal’, i.e a statistical infrequency. 
• Example: IQ and intellectual disability disorder 


  IQ is normally distributed. 

  The average IQ is 100. Most people have an IQ between 85-115, only 2% have a score below 70. 

  Those individuals scoring below 70 are statistically unusual or ‘abnormal’ and are diagnosed with intellectual disability disorder.