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Clinical Global Impression Scale-Severity (CGI-S)
Please visit this website for more information about the instrument: (forms on p. 218):

ECDEU Assessment Manual for Psychopharmacology

Supplemental: Parkinson's Disease (PD)
Short Description of Instrument
The Clinical Global Impression Scale-Severity (CGI-S) rating scale is a measure of symptom severity, originally developed for mental disorders, but now applied to various illnesses. This clinician-rated scale can be used in clinical practice and in research to track disease symptoms.
Comments/Special Instructions
A corresponding patient or participant version (or Patient Global Impression Scale-Severity; PGI-S) may be similarly structured but is reported by the patient or participant.
Scoring and Psychometric Properties
Scoring: The Clinical Global Impression Scale-Severity (CGI-S) is a 7-point categorical scale that 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. Clinicians ask: "Considering your total clinical experience with this particular population, how ill is the patient at this time?" Possible ratings are:
        1. Normal, not at all ill
        2. Borderline [mentally] ill
        3. Mildly ill
        4. Moderately ill
        5. Markedly ill
        6. Severely ill
        7. Among the most extremely ill patients

Psychometric Properties: Despite wide acceptance and use in clinical studies, psychometric properties of CGI-S have generally not been well established outside of psychiatric disorders. However, in Parkinson's disease CGI-S has been shown to correlate well with other global assessment scales (e.g., with a 0.91 correlation coefficient with the Clinical Impression of Severity Index scale) (Martínez-Martín, et al., 2016).
    • Simple
    • Brief
    • Integrative

    • Subjectively and imprecisely defined terms (e.g., severe illness) that require the rater to compare the patients or participants to typical ones in their clinical experience
    • Categorical scale with a small number of scale points reduces its capacity for resolution

No uniform guidance on administration
Key Reference:
Guy W. ECDEU Assessment Manual for Psychopharmacology. (Revised) Rockville, MD: U.S. Dept. 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. 1976.
Additional References:
Borgohain R, Szasz J, Stanzione P, Meshram C, Bhatt M, Chirilineau D, Stocchi F, Lucini V, Giuliani R, Forrest E, Rice P, Anand R; Study 016 Investigators.  Randomized trial of safinamide add-on to levodopa in Parkinson's disease with motor fluctuations. Mov Disord. 2014 Feb;29(2):229-37.
Busner J, Targum SD. The Clinical Global Impressions Scale: Applying a Research Tool in Clinical Practice. Psychiatry (Edgmont). 2007;4(7):28-37.
Martínez-Martín P, Rojo-Abuin JM, Rodríguez-Violante M, Serrano-Dueñas M, Garretto N, Martínez-Castrillo JC, Arillo VC, Fernández W, Chaná-Cuevas P, Arakaki T, Alvarez M, Ibañez IP, Rodríguez-Blázquez C, Chaudhuri KR, Merello M. Analysis of four scales for global severity evaluation in Parkinson's disease. NPJ Parkinsons Dis. 2016 May 5;2:16007.
Parkinson Study Group. Low-dose clozapine for the treatment of drug-induced psychosis in Parkinson's disease. N Engl J Med. 1999 Mar 11;340(10):757-63.
Document last updated August 2022