This article, published in Health Care Financing Review, finds that one third of Medicaid spending occurs in Medicaid-dominated markets including those surrounding mental health and long term care.  The article offers more detailed information on market share than was previously available for about half of the markets it assesses and discusses the implications of its findings. 

Quinn, K., & Kitchener, M. (2007). Medicaid's role in the many markets for health care. Health Care Financing Review, 28(4):69-82.  http://www.ncbi.nlm.nih.gov/pubmed/17722752

Authors: Kevin Quinn, Martin Kitchener.