Psychopathology

• Statistical infrequency


  Someone is mentally abnormal if their mental condition is very rare in the population, the rarity of the behaviour is judged objectively using statistics, comparing the individual's behaviour to the rest of the population
• Normal distribution curve


  • Shows a population's average spread of specific characteristics
  • The Mean Median and Modal scores are all at the highest point, the most common behaviour
  • At each end, there are fewer people with those behaviours
• Identifying abnormal behaviour


  1. Compare individuals to the population

  2. Identify those at the extreme ends
• Intelligence, measured by IQ

  • Average IQ is 100
  • Someone with an IQ two standard deviations from the average on either side is abnormal
  • One element of a diagnosis of intellectual disability disorder (IDD) in the DSM5 is having 70 IQ points or fewer
  • Just over 2% of the population is in this low intelligence bracket