Clinical Psychology - The branch of apllied psychology that deals with understanding and treating mental disorder
Statistical Definition Of Abnormality - The most literal way of defining something as abnormal is how often it occurs. Anyhting that occurs relatively rarely can be seen as abnormal.
Social Norms Definiton of Abnormality - There are commonly accepted standards of behaviour, some are written laws (no crime etc), and there are some unwritten customs, such as Queueing in the UK.
If someone was to deviate from these norms, it would be an indicator of abnormality. E.g. someone with OCD may wash their hands 50 times per day.
Schizophrenia - A psychcotic disorder which can leave the person out of touch with reality.
Reliability - The consistency with which a measure of a psychological variable like mental disorder identifies the same thing
Validity - The extent to which a measure of a psycholigcal variabe measures what it sset out to measure
A system can be said to be reliable if people usiong it consistently arrive at the same diagnosis. A way to test this is for 1 pateient to be assessed and diagnosed by different clinicians. This is known as inter-rater reliability. Another way to test reliability is to asses to same patient 2 or more times and see whether they consistently arrive at the same diagnosis. This is known as test-retest reliability. It is the most common way to judge reliability. Nicholls et al showed neither the ICD 10 or the DSM 4 demonstrated good inter rater reliability for the diagnosis of eating disorders in children. 81 patients between 7-16 classified using icd 10 and dsm 4. 50% couldnt be diagnosed using dms, reliability was 0.64 only due to most raters agreeing they couldnt make a diagnosis. icd was 0.36.
A dianostic system is valid ithe diagnosis successfully identifies a condition. There are several ways of defining validity in this context. It could be a system identifies a condition that will respond a particular way to treatment, this is known as predictive validity. It may be that the diagnosis agrees with a diagnosis made in a different way, this is known as criterion validity. Construct validity is the extent to which a category of mental disorder really exists. This might be called into question if the symptoms are similar to another condition. Allardyce questioned the construct validity of schizophrenia for 3 reasons.
1) although dellusions and hallucinations are bizarre experiences, theyre common in general public. no clear cut off point.
2)schizophrenia has a range of symptoms in different combinations thus individual patients with the diagnosis may appearvery different from one another.
3) it is unclear whether patients suffering from negative symptoms have the same condition as those suffering from positive symptoms.