According to the DSM-V, one must show at least 5 specific symptoms over a period of two weeks in order to be clinically diagnosed with major depressive disorder. One in particular that is absolutely essential to be shown in order for an individual to be diagnosed is of course a depressed mood, all day and nearly every day. Other symptoms may include Insomnia or hypersomnia nearly everyday/night and significant weight loss or gain; a 5% change in body weight must be seen in the space of a month. The individual may also have a diminished interest in pleasure nearly everyday, as well as feelings of worthlessness and excessive guilt. If an individuals shows less than 5 symptoms, they may be diagnosed with minor depressive disorder.
Reliability in Diagnosis
Diagnosis is made more reliable if more than one psychiatrist gives the same diagnosis to an individual, which is known as inter-rater reliability.
The most reliable diagnostic instruments are SCID-I/Ps, 60-90 minute semi-structured clinical interviews which start with open-ended questioning and gradually move to more systematic questioning regarding symptoms and current lifetime disorders. Clinical judgement is also required in order to interpret the patient's answer and to make a decision on the diagnosis.
Studies from Williams et al have found inter-rater reliability and diagnostic accuracy to be high, even when used by inexperienced interviewers. On the contrary, Beck studied 2 psychiatrists with 153 patients to diagnose, and found that inter-rater reliability was as low as 54%, suggesting that the diagnostic tool is not always reliable. Although SCID-I/Ps assess whether or not the patient scores on 5 or more of the DSM-V symptoms of depression, it does not assess the severity of those symptoms. Furthermore, each symptom is said to have a threshold, and therapists may disagree on whether or not this has been exceeded for a given patient.
As a result of these various issues a new method has recently been devised in order to improve the reliability of diagnosis, known as test-retest reliability. This refers to the same individual being tested at a later a date, by the same measure and receiving the same diagnosis.
One of the measures which has been tested is the Beck Depression Inventory (BDI), a 21-item self-report questionnaire. This method of test-retest reliability has been confirmed to be very effective by Beck himself, who found a significant correlation level of 0.93 using BDI for test-retest reliability. However, the reliability of these findings must be questioned due to the possibility of investigator bias, as Beck would of course be in favour of a method he created himself, and would therefore perhaps purposely highlight it to be highly effective in his own study.
There is also a possibility that the classification and diagnosis of depression is gender biased, as it has been proposed that there is no real difference between men and women suffering from depression. This is because while women are more likely to seek help for depression, men rarely do so and are therefore never included in the statistics. To support this, Bertakis et al found that clinicians in the Yale Family Study were more likely to diagnose women as depressed, even when the level of severity was equal to a man. This of course highlights that there may be a gender bias in diagnosis.
Additionally, knowing that both diagnostic systems were initially devised by white middle-class males indicates that they are potentially ethnocentric, as they are rooted in western societies. The characteristics for a person to be diagnosed as depressed are of course totally different across cultures. This was shown by Davidson and Neale, who found that Asian cultures encouraged individuals to show no emotion whilst experiencing turmoil, whilst Arabian cultures encouraged the outpouring of emotion at difficult times. Without this knowledge, individuals showing overt emotional behaviour in western societies may be deemed abnormal in this context.
Labelling and stigmatisation also appears to be a prevailing issue in the classification and diagnosis of depression. Psychiatrist Thomas Szasz argued that diagnosis is made on political and social backgrounds, and that this then leads to those who differ from society's norms being excluded from the mainstream population. Those with depression are therefore stigmatised by society once they are diagnosed, and will act in accordance to the label they are given in order to fit in.