Reliability & validity in diagnosis
- For a diagnosis of schizophrenia to be reliable it must show consistency and agreement across diagnosing clinicians i.e. the same set of symptoms must be given the same diagnosis regardless of who is doing the diagnosing
- Inter-rater reliability refers to the above point: if more than one clinician is diagnosing the same patient then they should both/all agree as to the diagnosis
- Issues with reliability occur when (as does happen) clinicians disagree as to the diagnosis
- Unreliable diagnosis may happen if clinicians do not use the same diagnostic tools e.g. one clinician uses the DSM and other uses the ICD, regardless of year of publication of both of these manuals
- Validity of diagnosis refers to the ‘realness’ of what is being measured i.e. is the classification system being used to diagnose the patient actually set up to diagnose schizophrenia or does it fall short of this criterion?
- An invalid diagnosis may occur if a clinician, having reviewed the patient’s symptoms, gives a diagnosis of an illness that does not actually fit those symptoms e.g. Sybil believes that she has multiple personalities and her doctor diagnoses schizophrenia (the correct diagnosis should be dissociative identity disorder)
Research which investigates reliability & validity in diagnosis
- Santelmann et al. (2016) conducted a meta-analysis of 25 studies with a total sample of 7912 patients diagnosed by different raters and found that reliability of schizophrenia diagnosis had consistently lower inter-rater reliability than the diagnosis of major depressive disorder and bi-polar disorder
- Rosenhan (1973) tested the validity of schizophrenia diagnosis in a field experiment in which he and eight confederates reported false symptoms and were all (but one) admitted to mental hospitals with a diagnosis of schizophrenia
Exam Tip
Make sure that you are clear as to the difference between reliability and validity (students often have a hard time distinguishing between the two and are often heard to vent their frustrations in class about how ‘annoying’ reliability/validity are - I’ve heard it many times!) In terms of schizophrenia diagnosis: reliability = do all doctors agree (DADA) and validity = Does It Seem Schizophrenic (DISS)? With apologies for the bad acronyms…
Do all patients receive a diagnosis that is both reliable and valid?