Issues surrounding the diagnosis and classificatio
This refers to the consistency of a measuring instrument. It can be assessed in terms of inter-rater reliability, which is when another psychologist get the same results and internal consistency.
There are a range of scales to measure OCD symptoms. There are general scales to measure anxiety levels and specific scales to measure obessessions and compulsions. The Yale- Brown Obessessive Compulsive Scale is a semi structured interview to assess symptoms, severity and responsiveness to treatment. Sections 1 and 2 ask patients what obssessions and compulsions they have experienced now or in the past. Section 3 has 10 short questions asking how the obssessions and compulsions interfere with daily functioning.
WOODY assessed 54 patients using Y-BOCS and found good internal consistency. Inter rater reliability was excellent. Test retest results after 48 days was lower than desirable, this might be due to the patient getting better or worse.
JAKES believes that there are sub groups of patients who differ in the nature of their obessession, it is suggested there may be different origins so may need different treatments.
This refers to the extent to which a diagnosis represents something which is real and distinct and the extent to which classification systems measure what they claim to measure.
Discriminant validity refers to the ability of a diagnosis to distinguish between OCD and other conditions. Rosenfield et al found patients diagnosed with OCD had higher Y-BOCS scored than those diagnosed with other anxiety disorders.
But WOODY found that patients diagnosed with OCD were also often diagnosed with depression. This is referred to as co morbidity; 67 percent of people with OCD also have depression.
Validity of diagnosis
It is possible that people do not produce honest answers to questionnaires about their symptoms which reduces the validity of the questionnaire, for example, they may be afraid that their answers might suggest deeper mental illness. They may lack awareness of the frequency and severity of symptoms, in this case validity might be improved by interviewing close friends or partners.
The symptoms are often shaped by patients culture of origin, for example a patient from a Western culture may have a contamination fear focused on germs, in India it may be focused on touching a person in a lower caste. This means that symptom checklists may be culturally biased.
WILLIAMS demonstrated that there were significant differences between normal populations of black and white Americans in scores of contamination obessessions. Research suggests black americans produce higher scores as they interact less with animals so have a greater concern about contamination with them. On the other hand MATSUNAGA studied japenese OCD patients and found symptoms and found symptoms similar to those in the west and concluded that OCD transcends cultures.