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Clinical Global Impression Scale-Improvement (CGI-I)
Please visit this website for more information about the instrument: (forms on p. 218): ECDEU Assessment Manual for Psychopharmacology
Supplemental - Highly Recommended:  Parkinson's Disease (PD)
Recommendations for use: Indicated for short-term intervention studies.
Short Description of Instrument
The Clinical Global Impression Scale-Improvement (CGI-I) rating scale is a measure of symptom response to treatment, or change (e.g., progression) over time. It was 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 of Improvement Scale; PGI-I) may be similarly structured but is reported by the participant.
Scoring and Psychometric Properties
Scoring: The Clinical Global Impression Scale-Improvement (CGI-I) is a 7-point categorical scale that is used by a clinician to assess how much the patient's or participant's illness has improved or worsened relative to a baseline state at the beginning of the study or intervention. Clinicians ask: "Compared to the patient's condition at baseline, this patient's [average] condition has...?" and rated as:

  1. Very much improved
  2. Much improved
  3. Minimally improved
  4. No change
  5. Minimally worse
  6. Much worse
  7. Very much worse


Psychometric Properties: Despite wide acceptance and use in clinical studies, psychometric properties of CGI have generally not been well established outside of psychiatric disorders.
  • Simple
  • Brief
  • Integrative

  • Subjectively defined terms 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.
Martinez-Martin P, Rojo-Abuin JM, Rodriguez-Violante M, Serrano-Duenas M, Garretto N, Martinez-Castrillo JC, Arillo VC, Fernandez W, Chana-Cuevas P, Arakaki T, Alvarez M, Ibanez IP, Rodriguez-Blazquez 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