for savings from preventive healthcare, and that the CBO had a track record of overestimating costs and underestimating savings of health legislation; stating, "innovations in the delivery of medical care, like greater use of electronic medical records and financial incentives for more coordination of care among doctors, would produce substantial savings while also slowing the relentless climb of medical expenses ... But the CBO would not consider such savings in its calculations, because the innovations hadn't really been tried on such large scale or in concert with one another—and that meant there wasn't much hard data to prove the savings would materialize." In 2010 David Walker stated that the CBO estimates were not likely to be accurate, because they were based on the assumption that the law would not change. Employer mandate and part-time work The employer mandate requires employers meeting certain criteria to provide health insurance to their workers. The mandate applies to employers with more than 50 employees that do not offer health insurance to their full-time workers. Critics claimed that the mandate created a perverse incentive for business to keep their full-time headcount below 50 and to hire part-time workers instead. However, between March 2010 and 2014 the number of part-time jobs declined by 230,000, while the number of full-time jobs increased by 2 million. In the public sector full-time jobs turned into part-time jobs much more than in the private sector. A 2016 study found only limited evidence that PPACA had increased part-time employment. Several businesses and the state of Virginia added a 29-hour-a-week cap for their part-time employees, to reflect the 30-hour-or-more definition for full-time worker. As of 2013, few companies had shifted their workforce towards more part-time hours (4% in a survey from the Federal Reserve Bank of Minneapolis). Trends in working hours and the recovery from the Great Recession correlate with the shift from part-time to full-time work. Other confounding impacts include that health insurance helps attract and retain employees, increases productivity and reduces absenteeism; and lowers corresponding training and administration costs from a smaller, more stable workforce. Relatively few firms employ over 50 employees and more than 90% of them already offered insurance. Most policy analysts (on both right and left) were critical of the employer mandate provision. They argued that the perverse incentives regarding part-time hours, even if they did not change existing plans, were real and harmful; that the raised marginal cost of the 50th worker for businesses could limit companies' growth; that the costs of reporting and administration were not worth the costs of maintaining employer plans; and noted that the employer mandate was not essential to maintain adequate risk pools. The provision generated vocal opposition from business interests and some unions who were not granted exemptions. Hospitals From the start of 2010 to November 2014, 43 hospitals in rural areas closed. Critics claimed that the new law had caused these closures. Many rural hospitals were built using funds from the 1946 Hill–Burton Act. Some of these hospitals reopened as other medical facilities, but only a small number operated emergency rooms (ER) or urgent care centers. Between January 2010 and 2015, a quarter of ER doctors said they had seen a major surge in patients, while nearly half had seen a smaller increase. Seven in ten ER doctors claimed that they lacked the resources to deal with large increases in the number of patients. The biggest factor in the increased number of ER patients was insufficient primary care providers to handle the larger number of insured. Several large insurers formed ACOs. Many hospitals merged and purchased physician practices, amounting