Describe and explain: Some symptoms of Schiz are also present in other mental disorders, making it hard to distinguish between them and for the diagnosis.
Example: Depression is also co-morbid with Schiz, ICD and DSM try to address this. Proposed mixed- disorder categories have been introduced.
Effects on reliability and'or validity and why? Mixed- disorder categories have questioned validity. they can be confusing, as the symptoms could be masking other symptoms, meaning the Psychiatrist may not be looking at the right thing- lacks interrater reliability.
Describe and explain: Rates of Schiz diagnosis is considerably different depending on what country you're in. shows what may be considered as Schiz on one country may in fact be different to another country, even when they are using the same classification tool.
Example: Copeland (1971)- 134 US and 194 British psychiatrists given a description of a patient. 69% of the US pshchiatrists and 2% of the British psychiatrists gave the diagnosis of Schiz.
Effects on reliability and/or validity and why: It makes the diagnosis tools fairly unreliable as the difference is huge. This also affects validity as the psychiatrists may be culturally bias, and therefore misdiagnose, which means the patient recieves incorrect treatment.
Availibility of other diagnostic criteria
Describe and explain: Should be consistent across the globe, but only some use it. Other diagnositic tools include Schnider Criteria, Research Diagnostic Criteria and St Louis Criteria. Using these can actually improve accuracy/reliability.
Example: Farmer et al (1988)- Increased levels of reliability when using standard interviewing techniques.
Effects on reliability and/or validity and why: It affects reliability and validity as some places are using the other diagnostic criteria and some aren't, meaning diagnosis rates are not the same where ever you go.
Lack of homogenity
Describe and explain: Symptoms aren't the same in all Schiz patients.
Example: Two patients with breast cancer be screened and told they both have the same kind of breast cancer, However two patients with hallucinations may not be the same.
Effects on reliability and/or validity and why: Affect validity of diagnosis as they might think it's adelusion not a hallucination. Might create complications with treatment.