Psychology RootsClinical Global Impression
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About Clinical Global Impression
Scale Name
Clinical Global Impression
Author Details
William Guy
Translation Availability
English
Background/Description
The Clinical Global Impression (CGI) scale is a widely used clinician-rated assessment tool designed to provide a concise, standardized evaluation of a patient’s overall psychiatric or medical condition severity, improvement, and treatment response. Developed by William Guy in 1976 as part of the ECDEU Assessment Manual for Psychopharmacology, the CGI was created to offer a flexible, clinician-friendly measure that could be applied across diverse mental health and medical conditions, including depression, anxiety, schizophrenia, and neurological disorders. Its simplicity and adaptability have made it a cornerstone in clinical trials and routine practice, where it captures a clinician’s holistic judgment of a patient’s status.
The CGI comprises three subscales: Severity of Illness (CGI-S), Global Improvement (CGI-I), and Efficacy Index (CGI-E). The CGI-S rates illness severity on a 7-point scale (1 = “normal, not at all ill” to 7 = “among the most extremely ill”). The CGI-I assesses improvement since baseline or treatment onset (1 = “very much improved” to 7 = “very much worse”). The CGI-E, less commonly used, evaluates therapeutic efficacy relative to side effects. Each subscale is completed based on the clinician’s observations, patient interviews, and collateral information, typically requiring minimal time. Its broad applicability stems from its non-specific design, allowing use in conditions ranging from mood disorders to chronic pain.
For psychologists, psychiatrists, and researchers, the CGI is invaluable for its brevity and ability to synthesize complex clinical data into a single, meaningful metric. It supports treatment planning, monitors progress, and facilitates communication in multidisciplinary settings. Its extensive translations enhance its global utility, ensuring clinicians worldwide can apply this versatile tool to improve patient outcomes with informed, evidence-based decisions.
Administration, Scoring and Interpretation
- Obtain a copy of the Clinical Global Impression scale from a reputable source, such as government health publications or authorized research platforms, ensuring ethical use.
- Explain the purpose of the CGI to the patient, noting that it helps clinicians assess their overall condition and treatment progress to guide care, though direct patient explanation may be minimal as it’s clinician-rated.
- Provide instructions, directing the clinician to rate the CGI-S based on the patient’s current state, CGI-I based on change since baseline, and CGI-E (if used) based on treatment benefits versus side effects, using clinical judgment and available data.
- Approximate time for completion is about 1-5 minutes per subscale, depending on the clinician’s familiarity with the patient’s history and condition.
- Administer the scale in a clinical setting, typically after a patient interview or observation, ensuring the clinician has sufficient information to make an informed rating.
Reliability and Validity
The Clinical Global Impression scale exhibits acceptable psychometric properties, though its subjective nature limits extensive statistical rigor compared to multi-item scales. Inter-rater reliability varies, with intraclass correlation coefficients typically ranging from 0.65 to 0.85 among trained clinicians, reflecting moderate to high agreement when standardized training is provided. Test-retest reliability is less frequently reported due to the scale’s focus on change, but short-term consistency is adequate (r = 0.70-0.80) in stable conditions.
Convergent validity is supported by moderate to strong correlations with disorder-specific measures, such as the Hamilton Depression Rating Scale (r = 0.60-0.75 for depression) or Positive and Negative Syndrome Scale (r = 0.65-0.80 for schizophrenia). Discriminant validity is evidenced by weaker correlations with unrelated constructs, like physical pain in psychiatric assessments (r < 0.40). Criterion validity is demonstrated by its sensitivity to treatment effects, with CGI-I scores reflecting improvement in clinical trials of antidepressants, antipsychotics, and anxiolytics. While less granular than specialized scales, the CGI’s broad applicability and clinical utility are well-established.
Available Versions
03-Items
Reference
Guy, W. (1976). ECDEU assessment manual for psychopharmacology. US Department of Health, Education, and Welfare, Public Health Service, Alcohol, Drug Abuse, and Mental Health Administration, National Institute of Mental Health, Psychopharmacology Research Branch, Division of Extramural Research Programs.
Important Link
Scale File:
Frequently Asked Questions
What does the CGI measure?
It measures illness severity, improvement, and treatment efficacy.
Who administers the CGI?
Trained clinicians, such as psychiatrists or psychologists, use it.
How long does the CGI take to complete?
It takes about 1-5 minutes per subscale.
Is the CGI specific to one disorder?
No, it’s used for various psychiatric and medical conditions.
Can the CGI guide treatment decisions?
Yes, it informs treatment planning and monitors progress.
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