One issue with diagnosing depression is Reliability. This is significant as when diagnosing and classifying depression over the classification systems such as the DSM IV and BDI, they must produce the same diagnosis for a set of symptoms for it to be considered reliable, therefore it must be consistent. This is tested using Inter Rater Reliability where different clinicians reach the same diagnosis when assessing the same individual independently, it is also tried using Test – Retest Reliability where the same tests should produce the same results for the same individual on two separate occasions.
Beck et al (1961) looked at the Inter Rater Reliability of the DSM between two psychiatrists when considering the cases of 154 patients. He found that it was actually quite low at 54%, this means that their diagnosis only agreed with each other for 54% of the 154 individuals. This suggests that they cannot diagnose consistently raising the issue of validity and how the disorder is not fully understood. However, Beck noted that in the 154 cases the patients gave different information to the two health professionals. Thus, a significant correlation cannot be established due to the patients giving information that is not relevant. Another study carried out by Keller et al (1995) consisted of a multi-site study which was designed to explore the reliability of the DSM classification system for Major Depressive Disorder and Dysthymia Disorder. 524 depressed individuals were recruited and interviewed using the DSM criteria for depression. They were then re-interviewed 6 months later in line with Test- Retest settings.
The results found that Inter Rater Reliability was ‘fair to good’ but the Test – Retest Reliability was only ‘fair suggesting when interviewing the same individuals the second time, the results had varied more. This was raising the concern about a lack of reliability and consistency over time. Additionally, Zanarini et al (2000) found that Inter – Rater Reliability for Major Depressive Disorder was 0.80 however Test – Retest settings saw this drop to 0.61 only a week after diagnosing the same individuals. This suggests that when professionals rely on retrospective data given by patients who may be struggling to recall information or are dishonest, this makes it inconsistent and unreliable which also undermines a reliable diagnosis. Also, practitioners have to make subjective choices based on their own interpretation of symptoms and criteria which will result in varied diagnoses.
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Another issue is Validity, this refers to whether a classification system is actually measuring what it is supposed to measure. Reliability and Validity are closely linked as if we cannot correctly diagnose something consistently then it is not considered valid or fully understood. The issue with Validity is the level to which many disorders overlap and there seems to be a growing trend in diagnosing individuals with ‘Co – Morbid’ disorders. This is when multiple disorders are seen to occur together which raises the issue that we may not fully understand Depression as many patients are diagnosed with multiple disorders and the primary disorder that should be treated may not be clear.
Research done by Kessler et al ( 1996) found that the chance of someone with a form of MDD suffering from any other disorder is 74% and an anxiety disorder was 58%. This calls into question the validity of depression as a diagnosis because of the many different types of disorders this highlights the difficulty in being able to differentiate between them and not knowing what to treat first in terms of the disorders.
Consequently a diagnosis of depression may have very little predictive validity as some people who may not respond well to treatments that target the wrong disorder first due to the professionals predicting the outcome and course of the disorder incorrectly. It may be possible that the Inter Rater Reliability has been found to be low due to the fact that the DSM criteria require 5 out of the 9 symptoms to be present in the patient. Because of this the severity of the disorder may be causing a disagreement between practitioners and could mean the difference between a less serious disorder or being diagnosed with MDD.
There is also the issue of Cultural Bias within the diagnosis and classification of Depression. It is assumed that the DSM and ICD that have been developed in the West, apply across all cultures. However this reflects the culture of white Europeans and so may not accurately assess people from other cultures. For example, Kua et al (1993) found that 72% of people in China who first presented with chest or abdominal pains or headaches were later found to have a mental health problem. So, they were not diagnosed properly by professionals which identifies that different cultures may follow different procedures which causes them to wrongly diagnose a patient.
