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The Clinical Global Impression Scale (CGI) is one of the most widely used brief rating scales in mental health and pharmaceutical trials. The CGI is a standardized assessment tool that allows the clinician to rate the severity of illness, change over time, and efficacy of medication; while taking into account the clients clinical condition and the severity of side effects. The CGI Scale is widely used in clinical psychopharmacology trials as an outcome measure. The CGI consists of three domains; Global Severity, Global Improvement, and Therapeutic Index. The Global Severity domain of the CGI is a single overall rating of severity of illness, which is rated on a seven-point scale rated from no mental illness to severely ill clients and change over time.  The CGI-Improvement is rated 1-7 from very much improved to very much worse (Jones et al., 2019).   This rating is based upon observed and reported symptoms, behavior, and function in the past seven days.  Symptoms and behaviors can fluctuate over a week; the score should reflect the average severity level during the seven days. The clinicians have many parameters to judge the severity of mental illness for clients in different settings.   However, the CGI is known for its ease of use and ability to track progress through time and is as effective as other more lengthy and tedious instruments (Jones et al., 2019). 
The CGI was developed as a simplified global measure to reflect the clinician’s view of the client’s condition before and after initiating medication.  The CGI tool is used to measure mental illness (medical history, psychosocial circumstances, symptoms, behaviors, and impact on functioning) to diagnose clients and measure the client’s response to treatment. For example, the CGI correlates well to scales such as the Hamilton Rating Scale for Depression, Hamilton Rating Scale for Anxiety, Positive and Negative Syndrome Scale, Brief Psychiatric Rating Scale to name a few (Jones et al., 2019).  
The CGI is well established and may be used for all psychiatric disorders in all FDA-regulated and most CNS trials; and the non-researcher clinician can easily use it in practice. The CGI is appropriate for use in depression, schizophrenia, anxiety, other mental disorders, regardless of the population, drug, or study measures. The CGI tool may also be used for other disorders such as sleep apnea (Dieltjens et al., 2019). The CGI is a brief and easy tool that may be administered by the practicing clinician to study the progression of treatment while using professional clinical judgment regarding the illness severity over the clinical experience. 
In conclusion, the Clinical Global Impression (CGI) is one of the most useful clinical tools available for monitoring outcomes across multiple clinically relevant domains, over time.  The CGI is valid, reliable, and easy to use. The CGI can be effectively and efficiently used across cultures, for clients of all ages and across socio-economic locations, and mental disorders.  The CGI scale allows the APPN to provide a more comprehensive treatment plan by creating a quantifiable measurement of symptoms and treatment efficacy. The clinician can monitor symptoms and improvement or lack of, to determine if the client is getting better or not throughout treatment.  Therefore, allowing the client and provider to make an informed decision providing patient-centered treatment utilizing evidence-based practice.