How can mental disorders be defined?

Mental disorders can be defined in a number of ways. One mathematical way it can be defined is a deviation from statistical norms. This means that a mental disorder is categorised as being either above or below 2 standard deviations from the mean, where 'normal' behaviours would fall within this region. It can be represented as the tail ends of a bell curve, where the very top and very bottom are considered 'abnormal'. Another way is deviation from social norms. In this case, social norms are socially accepted behaviours which are created by society, a simple example could be standing on one particular side of the staircase. This definition states that a large deviation from acceptable behaviour in society can be considered abnormal, particularly if it causes others distress. Also, mental disorder can be defined in terms of ability to cope, also known as maladaptive behaviours. This can be measured in a checklist form to assess whether someone is able to complete day-to-day tasks such as getting out of bed and eating 3 meals a day. A clinical psychologist could then make a decision based on this inability to complete activities as to whether someone has a poor mental health.