When considering deviance from a statistical point of view, one potential strength is that it allows people to be compared objectively and means that a value-free judgement can be made where all people are considered equally without influence of gender or ethnicity for example. This is because you can plot their score on a normal distribution curve to see how it compares to the mean; a z score of >+2/-2 would indicate that a person’s behaviour deviates sufficiently from the norm to indicate that a diagnosis may be helpful, thus allowing cases to be prioritised fairly.

One weakness of using deviation alone to identify those in need of diagnosis is that sometimes a behaviour or way of life may well deviate from statistical norms and may seem unusual within a society’s typical patterns of behaviour, however, the individual themselves may not feel distressed by this difference and may continue to function very well. For example some rare behaviours are seen as socially desirable such as great musical or mathematical ability and therefore deviation from the norm is not enough to warrant the label of abnormality.