This was meant to assess the patient's functioning prior to and after initiating medication in trials which is an important part of study process.
Despite its wider acceptance and consistent use in clinical trials, psychometric properties of CGI have not been established.
Its sensitivity is good enough to differentiate between responders and non-responders in clinical trials of depression,[6] but its specificity is not satisfactory.
It has poor interrater reliability than HAM-D.[7] Many weaknesses could explain this possible lack of validity of the CGI: there is no specific interviewer guide available, and while most other symptoms scales have fairly clear and specific response options, the response format used in the CGI to assess change or severity of illness is more likely to be ambiguous (what is the definition of a patient who is "Severely ill"?).
[8] The clinical global impression – severity scale (CGI-S) is a 7-point 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.