A depression rating scale is a psychiatric measuring instrument having descriptive words and phrases that indicate the severity of depression symptoms for a time period. When used, an observer may make judgements and rate a person at a specified scale level with respect to identified characteristics. Rather than being used to diagnose depression, a depression rating scale may be used to assign a score to a person's behaviour where that score may be used to determine whether that person should be evaluated more thoroughly for a depressive disorder diagnosis. Several rating scales are used for this purpose.
Scales completed by researchers
Some depression rating scales are completed by researchers. For example, the Hamilton Depression Rating Scale includes 21 questions with between 3 and 5 possible responses which increase in severity. The clinician must choose the possible responses to each question by interviewing the patient and by observing the patient's symptoms. Designed by psychiatrist Max Hamilton in 1960, the Hamilton Depression Rating Scale is one of the two most commonly used among those completed by researchers assessing the effects of drug therapy. Alternatively, the Montgomery-Åsberg Depression Rating Scale has ten items to be completed by researchers assessing the effects of drug therapy and is the other of the two most commonly used among such researchers. Other scale is the Raskin Depression Rating Scale; which rates the severity of the patients symptoms in three areas: verbal reports, behavior, and secondary symptoms of depression.
Scales completed by patients
Some depression rating scales are completed by patients. The Beck Depression Inventory, for example, is a 21-question self-report inventory that covers symptoms such as irritability, fatigue, weight loss, lack of interest in sex, and feelings of guilt, hopelessness or fear of being punished. The scale is completed by patients to identify the presence and severity of symptoms consistent with the DSM-IV diagnostic criteria. The Beck Depression Inventory was originally designed by psychiatrist Aaron T. Beck in 1961.
The Geriatric Depression Scale (GDS) is another self-administered scale, but in this case it is used for older patients, and for patients with mild to moderate dementia. Instead of presenting a five-category response set, the GDS questions are answered with a simple "yes" or "no". The Zung Self-Rating Depression Scale is similar to the Geriatric Depression Scale in that the answers are preformatted. In the Zung Self-Rating Depression Scale, there are 20 items: ten positively-worded and ten negatively-worded. Each question is rated on a scale of 1 through 4 based on four possible answers: "a little of the time", "some of the time", "good part of the time", and "most of the time".
The Patient Health Questionnaire (PHQ) sets are self-reported depression rating scales. For example, the Patient Health Questionnaire-9 (PHQ-9) is a self-reported, 9-question version of the Primary Care Evaluation of Mental Disorders. The Patient Health Questionnaire-2 (PHQ-2) is a shorter version of the PHQ-9 with two screening questions to assess the presence of a depressed mood and a loss of interest or pleasure in routine activities; a positive response to either question indicates further testing is required.
Scales completed by patients and researchers
The Primary Care Evaluation of Mental Disorders (PRIME-MD) is completed by the patient and a researcher. This depression rating scale includes a 27-item screening questionnaire and follow-up clinician interview designed to facilitate the diagnosis of common mental disorders in primary care. Its lengthy administration time has limited its clinical usefulness.
Screening programs using rating scales to search for candidates for a more in-depth evaluation have been advocated to improve detection of depression, but there is evidence that they do not improve detection rates, treatment, or outcome. There is also evidence that a consensus on the interpretation of rating scales, in particular the Hamilton Rating Scale for Depression, is largely missing, leading to misdiagnosis of the severity of a patients depression. 
- Diagnostic classification and rating scales used in psychiatry
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