PROJECT SUMMARY Serious mental illness affects more than 5% of the United States population, but only a small proportion of these individuals receive adequate treatment. Schizophrenia impacts one percent of the population and is particularly debilitating. Individuals with schizophrenia have high rates of poor health and social outcomes, including premature mortality, homelessness, and substance use. Individuals with schizophrenia are at increased risk of suicide and have high rates of comorbid disease. Guideline-concordant care (GCC) ? including appropriate medications and psychotherapy ? improves outcomes for individuals with schizophrenia, including mortality. However, rates of GCC are low, with significant variation across patient demographic groups, clinical conditions, and clinician types. Although some differences may be explained by patient preferences, system factors at the insurance and organization levels likely contribute to low rates of GCC. Better understanding system factors ? including the role of insurance networks and organizations ? that help guide treatment pathways towards GCC and improve patient outcomes is an important contribution to improving clinical practice for individuals living with schizophrenia. Pursuant to the goals of PAR-19-189, the objective of this pilot services research is to identify mutable health care system factors related to access and quality of mental health services. Using comprehensive health insurance enrollment and claims data from Massachusetts we quantify and examine variation in insurance networks for those with schizophrenia, examine associations of these network characteristics ? including size and composition (reflecting availability of mental health clinicians) ? with patient outcomes of guideline-concordant care receipt and self-harm. As a potential mechanism for understanding how insurance networks may influence patient outcomes, we examine associations of organizational characteristics ? organization size and proportion of mental health clinicians ? with patient outcomes. We conduct sensitivity analyses limiting to individuals with first episode psychosis due to the clinical urgency of comprehensive care and policy interest in this population, and establish a causal relationship between insurance networks and organizations and outcomes using a young adult sample. Understanding factors associated with GCC and outcomes will help identify effective policy levers to improve care. Findings from this pilot study will guide future improvements in mental health services delivery, as well as identify avenues for future research on policy changes influencing critical system characteristics.