statistical infrequency

• 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.
• Distribution curve


  The 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. If we want to find abnormal behaviour, we can compare individuals to the population and identify those at the extreme ends.
• Example

  Intelligence - measured by IQ.

  The average IQ is 100, at this graph's highest point. Someone with an IQ two standard deviations from the average on either side is abnormal. One element of a diagnosis of intellectual disability disorder in the DSM5 is having 70 IQ points or fewer. Just over 2% of the population is in this low intelligence bracket.
• / Some abnormal behaviours are desirable


  E - Having an IQ over 150 is abnormal. This does not make it a bad thing.

  E- Many people desire having a high IQ, but people with one are seen as abnormal.

  L - Therefore, the definition of statistical infrequency does not account for desirable behaviours.
• / Inflexible definition


  E - It states that scores in the top and bottom 2.5% of the population are abnormal, but we know that there is some behaviour which is deemed abnormal by the diagnostic manuals for mental illness that would not fit within that definition.

  E - This means that the definition and the current criteria for defining mental health issues are at odds with each other.

  L - Therefore, this can show that the definition is widely inflexible and sometimes not applicable.
• + Objective


  E - The mathematical nature of this definition means that it is clear what is defined as abnormal and what is not.

  E - There is no opinion involved which means there is no bias.

  L - Therefore, this is better than other definitions that depend on the subjective opinion of a clinician.
• / Abnormal behaviours can occur frequently


  E - Depression is an example, where it is argued that 25% of the population will experience a mental health issue at some point in their lives.

  E - It is not the case that abnormal, as in unhelpful and painful, behaviours occur rarely.

  L - Therefore, this definition is not appropriate when considering society's high incidence of mental health disorders.