Statistical Infrequency (AQA A Level Psychology): Revision Note

Statistical infrequency

• Statistical infrequency (or statistical deviation as it is also known) defines abnormal behaviour using statistical measures

• A behaviour is regarded as abnormal if it is statistically uncommon/rare in that it is not present often or regularly per society e.g.:

  • The average IQ is approximately 100

    • 95% of the population have an IQ which falls between 70 to 130

    • approximately 2.5% of the population have an IQ below 70

    • approximately 2.5% of the population have an IQ of 130⁺

  • About 1 in 300 (0.33%) people worldwide have schizophrenia, making it an abnormal condition/illness

• Rare behaviours/conditions are considered statistically abnormal for example:

  • the case of HM who suffered extreme anterograde amnesia of a type which is highly unique and unusual

• Behaviour can be measured as normal or abnormal according to where it is placed within a normal distribution

• A distribution curve (graph) can be used to represent the proportions of a population who share a particular characteristic, e.g. IQ

Evaluation of statistical infrequency for A Level Psychology

Strengths

• Statistical infrequency as a measure of abnormality provides clear points of comparison between people, making it easy to test and to use as an analytical tool e.g.:

  • if person X scores 70 on an IQ test this falls a long way below the mean average for the population 

    • This statistically infrequent score indicates that extra help or interventions may be required for the person in question

• Applying statistical infrequency as a measure includes the use of a standardised tool which means that the measure has built-in reliability

  • Standardised measures are replicable i.e. they can be applied repeatedly to analyse data sets

  • Replicability means that large data sets can be included in the calculation

  • The larger the data set, the less likely it is to be affected by outliers/anomalous results thus consistent patterns/trends are highlighted and consistency = reliability

Limitations

• Statistical infrequency would not recognise depression as abnormal behaviour

  • Depression is estimated to affect around 280 million people across the world at any given time

    • the high prevalence rate of depression means that it is not statistically deviant

    • if depression is not statistically deviant then SI is not a fully valid measure of abnormality

• One statistically infrequent behaviour which is not necessarily undesirable or adverse is having an IQ of 175

  • A high IQ is classified as statistically infrequent yet it could not be argued that having a high IQ is undesirable or limiting in the same ways as having a low IQ would be

  • This mismatch in the measure limits the usefulness of statistical infrequency