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Clinical Global Impression (CGI)

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National Institute of Mental Health. CGI: Clinical Global Impressions. In: Guy W, Bonato RR, eds. Manual for the ECDEU Assessment Battery.2. Rev ed. Chevy Chase, Md: National Institute of Mental Health; 1970:12-1-12-6.

Appropriate for: All categories of psychiatric patients
Administered by: Patient's psychiatrist or other trained rater
Time to complete: 5 minutes

CGI is a three-item scale used to assess treatment response in psychiatric patients. They are:
Severity of Illness; Global Improvement; Efficacy Index. Item 1 is rated on a seven-point scale (1=normal to 7=extremely ill); item 2 on a seven-point scale (1=very much improved to 7=very much worse); and item 3 on a four-point scale (from 'none' to 'outweighs therapeutic effect').

The Severity of Illness item requires the clinician to rate the severity of the patient's illness at the time of assessment, relative to the clinician's past experience with patients who have the same diagnosis. Considering total clinical experience, a patient is assessed on severity of mental illness at the time of rating according to: normal (not at all ill); borderline mentally ill; mildly ill; moderately ill; markedly ill; severely ill; or extremely ill.

The Global Improvement item requires the clinician to rate how much the patient's illness has improved or worsened relative to a baseline state. Compared to condition at baseline, a patient's illness is compared to change over time, and rated according to: very much improved; much improved; moderately improved; minimally improved; no change; minimally worse; moderately worse; much worse; or very much worse.

Benefits of the CGI scale:

  • Robust - CGI has proved to be a robust measure of efficacy in drug treatment trials
  • Simplicity - the scale is clinically understandable
  • Sensitive to change

Challenges of the CGI scale:

  • Subjective - to a certain degree, severity of illness as rated on the CGI scale is based on the rater's subjective views of symptom severity, which can vary between raters and make consistent interpretation of CGI scores problematic in practice
  • Lack of structure - the CGI scale is administered at initial patient assessment and at least once when treatment/change in treatment has been initiated. Additional assessments are conducted at the discretion of the clinician. Again, this implies a certain degree of subjectivity in terms of the timing and frequency of CGI assessment which may make retrospective interpretation difficult
  • In-depth knowledge required - although the CGI scale is quickly administered, particularly for the Global Improvement scale it is paramount for the rater to know the patient. If a clinical history is not available, then the tool can not be utilised


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