Most psychological disorders are diagnosed on the basis of clinical symptoms. Psychological disorders though, are highly subjective to biases of the psychiatrist and thus may result in a problem with the diagnosis. Clinical biases may result because of diverse reasons. Cross- cultural variations for example. Different cultures may consider different behaviours as normal or abnormal therefore a psychologist may interpret behaviours differently based on the cultural background they grew up with. Duncan Double (2006) argues the frequent occurrence of over diagnosis in diagnosing psychological disorders. Thus occurs when patients suggest themselves a disorder which they might suffer& The doctor, lacking evidence for a diagnosis fulfils the patients want by over-diagnosing. This diagnostic bias tends to happen when the symptoms in the patients are unexplained. Another known clinical bias is the confirmation bias. Thus occurs when a psychologist seeks, interprets and remembers information so that it confirms their preconceptions. This leads the researcher to weight more evidence that supports his/hers hypothesis and disregard evidence that denies it.
The study conducted by Mendel et al in 20 aimed to see if psychologists would show confirmation bias when making a diagnosis. The researcher used purposive sampling and tested 75 psychiatrists and 75 medical students. All participants
were given a summary of a case study that focused on an elderly man who suffered from Alzheimers. Though the man originally suffered from Alzheimers disease, the summary of the case study made it seem as most probable that he suffered from depression. After reading the case study, all participants were allowed to conduct further research. Results showed that 3% of the psychiatrists and 25% of the medical students misdiagnosed the individual due to the preconception they had on the diagnosis. This study concluded that clinicians are subjected to confirmation biases and therefore their diagnosis may be influenced by their conceptions of an individuals attitudes. The study conducted by Mendel provides insightful knowledge on regards to studying social groups and the study was able to analyse participants behaviour without them knowing it was an investigation (reducing participant bias). On the other hand, the study conducted by Mendel shows some limitation as confirmation bias is a very subjective thing, that changes from person to person, affecting people in a different manner. Thus would affect the generalisability of the data gathered from the investigation. Clinicians who diagnosed the elderly man with depression suggested and prescribed wrong treatments endangering the individual, therefore this study shows how confirmation bias can lead to harmful and dangerous diagnosis.