Statical infrequency:

• STRENGTH:

  • is its usefulness
  • 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
  • IE: a diagnosis of intellectual disability disorder requires an IQ of below 70 (bottom 2%).
  • An example of statistical infrequency used in an assessment tool is the Beck depression inventory (BDI). A score of 30+ (top 5% of respondents) is widely interpreted as indicating severe depression

  This shows that the value of the statistical infrequency criterion is useful in diagnostic and assessment processes.
• LIMITATION:

  • infrequent characteristics can be positive as well as negative
  • For every person with an IQ below 70 there is another with an IQ above 130
  • Yet we would not think of someone as abnormal for having a high IQ
  • Similarly we would not think of someone with a very low depression score on the BDI as abnormal
  • 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.