Clinical global impression

Validity of CGI scales

Despite its wider acceptance and consistent use in clinical trials, psychometric properties of CGI have not been established. However, the scale is found to be valid as an external criterion during the development of scales of depression and anxiety. In many studies, the clinicians' ratings of psychiatric symptoms were found to correlate significantly with self-rated and other valid scales of symptom severity. For example, Leon et al. (1993) showed that severity ratings but not improvement ratings were predicted highly and significantly by frequency of panic attacks, depression and anxiety ratings made on already valid rating scales. Similarly, another study showed that MADRS, HAM-D and CGI scales had comparable effect sizes and could be equally used in studies to assess severity and improvement of symptoms. Even though many studies have established the validity of CGI scales in relation to other commonly used robust rating scales, its efficacy in predicting treatment outcomes is highly debated. Its sensitivity is good enough to differentiate between responders and non-responders in clinical trials of depression, but its specificity is not satisfactory. It has poorer interrater reliability than HAM-D. 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"?).