How are Validity & Reliability Relevant to Diagnosis? (SL IB Psychology)

• For a mental illness diagnosis to be valid it must accurately reflect the patient’s symptoms, free from bias (clinical biases in diagnosis are covered in a separate revision note)
• A valid diagnosis is one which should classify and describe a genuine pattern of symptoms resulting from a real underlying cause
• A valid diagnosis will result in appropriate treatment being prescribed with the expectation of improvement and progress as a result of this treatment
• Due to the complex nature of mental illness the diagnostic process is not always straightforward e.g. is the patient’s low mood due to depression, anxiety, OCD or could it be part of a potentially more serious disorder such as schizophrenia?
• It is arguably more difficult for a clinician to diagnose a specific mental illness than it is for them to diagnose a physical illness e.g. Covid-19 is detectable by testing saliva; a broken bone shows up on an X-ray

Diagnosing mental illness is a complex process…

• For a mental illness diagnosis to be reliable there should be agreement and consistency across different diagnostic settings i.e. the same diagnosis for the same symptoms presented by the same patient should be made, regardless of who is in charge of the diagnosis
• Classification systems such as the DSM-5 and the ICD 11 aim to standardise diagnostic criteria so as to ensure built-in reliability
• Due to the complex nature of mental illness the likelihood of symptom overlap is common, making reliable diagnosis problematic e.g. if a patient reports hearing voices along with the compulsion to wash their hands every 10 minutes this may result in one diagnosis of schizophrenia whereas another clinician may diagnose OCD
• Patients who are comorbid may find that the treatment prescribed is based on only one of their disorders rather than taking both of them into consideration (e.g. SSRIs for their depression but nothing for their social phobia)
• The symptoms of mental illnesses are difficult to measure as they are experienced subjectively and may even defy measurement (e.g. how can delusions be measured objectively?) which is a challenge when it comes to making a reliable diagnosis

Which studies investigate validity & reliability of diagnosis?

• Rosenhan et al. (1973) - mental illness diagnosis may not be valid and may result in people being stigmatised

• Nicholls et al. (2000) - eating disorders in children are not diagnosed reliably and the process needs to be reviewed

Both Rosenhan et al. (1973) and Nicholls et al. (2000) are available as Two Key Studies of Validity & Reliability of Diagnosis – just navigate the Factors Influencing Diagnosis section of this topic to find them.