INTRODUCTION: The inflammation observed in patients with IBD can negatively impact the intake or absorption of vitamin D. This can increase the risk of disease relapse, impact patients’ quality of life, and increase the risk of IBD related surgeries. In addition to the traditional observation that vitamin D deficiency may be a comorbid manifestation of IBD, there is now growing evidence pointing to serum vitamin D levels as a pathogenic factor contributing to the initiation and propagation of mucosal inflammation in patients with IBD. It is well-established that variation in clinical practice leads to less optimal outcomes in any clinical setting. The relative scarcity of clinical and translational studies is even more pronounced in the pediatric population. OBJECTIVES: The primary objective of this study is to quantify the prevalence of clinician assessment of vitamin D levels in pediatric patients with IBD. We will also look at this behavior in subpopulations and compare their vitamin D status. It is secondary for this study to also describe variations in physician practices with respect to the testing and treatment of vitamin D deficiency at a single tertiary care IBD Center. METHODS: We conducted a retrospective cohort study on consecutive patients with UC, CD, and ID, that were followed in the ambulatory program in the Center for Inflammatory Bowel Disease at Boston Children’s Hospital from 1/1/2014 to 12/31/2014. We identified 498 patients and collected their demographic information, serologic testing, and physician prescribing behavior. RESULTS: Out of the entire population, 64% of the patients were vitamin D deficient (vitamin D level below 32 ng/ml). 24% of the patients received vitamin D supplementation. Vitamin D deficiency was less prevalent in patients with UC than those with CD, with an OR of 0.64 (95% CI 0.43-0.94). Out of the ones receiving supplementation, 37% of them were deficient. In terms of physician practice trends, 62% of the patients were not formally prescribed supplementation. 14.5% of those who were prescribed supplementation were receiving 50,000 IU weekly, and the rest receiving 400 – 2,000 IU daily. Patients with vitamin D levels below 20 ng/ml were more likely to receive the high dose vitamin D prescription (OR 11.5) than those with levels between 20 and 30 ng/ml (OR 5.7). CONCLUSIONS: Our study suggests that despite high prevalence of vitamin D deficiency in pediatric patients with IBD, there is a lack of consensus with respect to the assessment of vitamin D levels and consistency in prescribing vitamin D supplementation. With the potential role that vitamin D plays in IBD pathology and suggestions of the therapeutic effects of vitamin D supplementation, further studies are needed to explore this area.

Understanding how health care markets function is important not only because competition has a direct influence on the price and utilization of health care services, but also because the proper functioning, or lack thereof, of health care markets has a very real impact on patients who depend on health care markets and providers for their personal well-being. In this dissertation, I examine the role of government policies and regulation in health care markets, with a focus on the response of health care providers. In Chapter 1, I analyze the impact of Medicare payment rules on hospital ownership of physician practices. Since the mid-2000’s, there has been a rapid increase in hospital ownership of physician practices, however, there is little empirical research which addresses the causes of this recent wave of integration. Medicare’s “provider-based” billing policy allows hospital-owned physician practices to charge higher reimbursement rates for services provided compared to a freestanding, independent physician practice, without altering how or where services are provided. This “site-based” differential creates a premium for physicians to integrate with hospitals, and the size of this differential varies with the types of health care services provided. I find that Medicare payment rules have contributed to hospital ownership of physician practices and that the response varies across physician specialties. A 10 percent increase in the relative reimbursement rate paid to integrated physicians leads to a 1.9 percentage point increase in the probability of hospital ownership for Medical Care specialties, including cardiology, neurology, and dermatology, which explains about one-third of observed integration of these specialties from 2005 through 2015. Magnitudes for Surgical Care specialties are similar, but more sensitive across specifications. There is no significant response for Primary Care physicians. In combination with other empirical literature which finds that integration between physicians and hospitals typically results in higher prices with no impact on costs or quality of care, I cautiously interpret this responsiveness as evidence that Medicare’s provider-based billing policy overcompensates integrated physician practices and leads to an inefficiently high level of vertical integration between physician and hospitals. In Chapter 2, I analyze the effect of anti-fraud enforcement activity on Medicaid spending, with a particular focus on the False Claims Act. The False Claims Act (FCA) is a federal statute which protects the government from making undeserved payments to contractors and suppliers. Individual states have chosen to enact their own versions of the federal FCA, and these statutes have increasingly been used to target health care fraud. FCA statutes commonly include substantial monetary penalties such as “per-violation” monetary fines and tripled damages, as well as a “whistleblower” provision which allows private plaintiffs to initiate a lawsuit and collect a portion of recoveries as a reward. Using variation in statelevel FCA legislation, I find state FCAs reduce Medicaid prescription drug spending by 21 percent, while other spending categories - which are less lucrative for FCA lawsuits - are unresponsive. Within the prescription drug category, drugs prone to off-label use show larger declines in response to the whistleblower laws, consistent with FCA lawsuits being used to prosecute pharmaceutical manufacturers for off-label marketing and promotion. Spending and prescription volume for drugs prone to off-label use fall by up to 14 percent. This effect could be driven by pharmaceutical manufacturers’ changes in physician detailing for drugs prone to off-label use and/or physicians’ changes in prescribing behavior.