CHAPTER 1. INTRODUCTION CHAPTER 2. LITERATURE REVIEW Efficacy of Psychotherapy CHAPTER 2 LITERATURE REVIEW The number of individuals living with or at risk for developing a mental illness is staggering. Approximately one out of every four individuals experiences mental illness in a given year (Clement et al., 2015). Of those, approximately half are diagnosed with two or more disorders. In a recent study conducted by The World Health Organization (WHO), mental illness and suicide accounted for over fifteen percent of the years of life lost to mortality and to time lost to ill health in the United States. This is more than the disease burden caused by all cancers combined (WHO, 2004). In line with this, Demyttenaere and colleagues (2004) studied the prevalence, severity and treatment of Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) mental disorders in 14 countries (6 less developed, 8 developed) in the WHO's World Mental Health (WMH) Survey Initiative. Researchers conducted face-to-face household surveys of 60,463 community adults from 2001 to 2003 in 14 countries in the Americas, Europe, Middle East, Africa and Asia. Within the United States, of the individuals surveyed, 18.2% met criteria for anxiety disorders, 9.6% mood disorders, 6.8 impulse control disorders, 3.8% for substance use and 26.4 for any disorder. Of those who met criteria, 52.3% of those with an illness categorized as serious received health care treatment, 34.1% with moderate categorization received treatment and 22.5% with a mild disorder received treatment. Serious cases included serious lethal suicide attempts within the past 12 months, work limitations due to mental illness or substance disorders, symptoms of psychosis, bipolar disorders, substance dependence that impacted daily functioning, serious repeated violence due to problems with impulse control, and mental illness that resulted in 30 or more days out of life roles (Demyttenaere, Bruffaerts,