dramatically, from 47 million to 79 million, and the ratio of workers to enrollees is expected to decrease from 3.7 to 2.4. however, the ratio of workers to retirees has declined steadily for decades, and social insurance systems have remained sustainable due to rising worker productivity. there is some evidence that productivity gains will continue to offset demographic trends in the near future. the congressional budget office (cbo) wrote in 2008 that "future growth in spending per beneficiary for medicare and medicaid—the federal government's major health care programs—will be the most important determinant of long-term trends in federal spending. changing those programs in ways that reduce the growth of costs—which will be difficult, in part because of the complexity of health policy choices—is ultimately the nation's central long-term challenge in setting federal fiscal policy." overall health care costs were projected in 2011 to increase by 5.8 percent annually from 2010 to 2020, in part because of increased utilization of medical services, higher prices for services, and new technologies. health care costs are rising across the board, but the cost of insurance has risen dramatically for families and employers as well as the federal government. in fact, since 1970 the per-capita cost of private coverage has grown roughly one percentage point faster each year than the per-capita cost of medicare. since the late 1990s, medicare has performed especially well relative to private insurers. over the next decade, medicare's per capita spending is projected to grow at a rate of 2.5 percent each year, compared to private insurance's 4.8 percent. nonetheless, most experts and policymakers agree containing health care costs is essential to the nation's fiscal outlook. much of the debate over the future of medicare revolves around whether per capita costs should be reduced by limiting payments to providers or by shifting more costs to medicare enrollees. indicators several measures serve as indicators of the long-term financial status of medicare. these include total medicare spending as a share of gross domestic product (gdp), the solvency of the medicare hi trust fund, medicare per-capita spending growth relative to inflation and per-capita gdp growth; general fund revenue as a share of total medicare spending; and actuarial estimates of unfunded liability over the 75-year timeframe and the infinite horizon (netting expected premium/tax revenue against expected costs). the major issue in all these indicators is comparing any future projections against current law vs. what the actuaries expect to happen. for example, current law specifies that part a payments to hospitals and skilled nursing facilities will be cut substantially after 2028 and that doctors will get no raises after 2025. the actuaries expect that the law will change to keep these events from happening. total medicare spending as a share of gdp medicare cost and non-interest income by source as a percentage of gdp this measure, which examines medicare spending in the context of the us economy as a whole, is projected to increase from 3.7 percent in 2017 to 6.2 percent by 2092 under current law and over 9 percent under what the actuaries really expect will happen (called an "illustrative example" in recent-year trustees reports). the solvency of the medicare hi trust fund this measure involves only part a. the trust fund is considered insolvent when available revenue plus any existing balances will not cover 100 percent of annual projected costs. according to the latest estimate by the medicare trustees (2018), the trust fund is expected to become insolvent in 8 years (2026), at which time available revenue will cover around 85 percent of annual projected costs for part a services. since medicare began, this solvency projection has ranged from two to 28 years, with an average of 11.3 years. this and other projections in medicare trustees reports are based on what its actuaries call intermediate scenario but the reports also include worst-case and best-case projections that are quite different (other scenarios presume congress will change present law). medicare per-capita spending growth relative to inflation and per-capita gdp growth per capita spending relative to inflation per-capita gdp growth was to be an important factor used by the ppaca-specified independent payment advisory board (ipab), as a measure to determine whether it must recommend to congress proposals to reduce medicare costs. however, the ipab never formed and was formally repealed by the balanced budget act of 2018. general fund revenue as a share of total medicare spending this measure, established under the medicare modernization act (mma), examines medicare spending in the context of the federal budget. each year, mma requires the medicare trustees to make a determination about whether general fund revenue is projected to exceed 45 percent of total program spending within a seven-year period. if the medicare trustees make this determination in two consecutive years, a "funding warning" is issued. in response, the president must submit cost-saving legislation to congress, which must consider this legislation on an expedited basis. this threshold was reached and a warning issued every year between 2006 and 2013 but it has not been reached since that time and is not expected to be reached in the 2016–2022 "window". this is a reflection of the reduced spending growth mandated by the aca according to the trustees. unfunded obligation medicare's unfunded obligation is the total amount of money that would have to be set aside today such that the principal and interest would cover the gap between projected revenues (mostly part b premiums and part a payroll taxes to be paid over the timeframe under current law) and spending over a given timeframe. by law the timeframe used is 75 years though the medicare actuaries also give an infinite-horizon estimate because life expectancy consistently increases and other economic factors underlying the estimates change. as of january 1, 2016, medicare's unfunded obligation over the 75-year time frame is $3.8 trillion for the part a trust fund and $28.6 trillion for part b. over an infinite timeframe the combined unfunded liability for both programs combined is over $50 trillion, with the difference primarily in the part b estimate. these estimates assume that cms will pay full benefits as currently specified over those periods though that would be contrary to current united states law. in addition, as discussed throughout each annual trustees' report, "the medicare projections shown could be substantially understated as a result of other potentially unsustainable elements of current law." for example, current law effectively provides no raises for doctors after 2025; that is unlikely to happen. it is impossible for actuaries to estimate unfunded liability other than assuming current law is followed (except relative to benefits as noted), the trustees state "that actual long-range present values for (part a) expenditures and (part b/d) expenditures and revenues could exceed the amounts estimated by a substantial margin." public opinion popular opinion surveys show that the public views medicare's problems as serious, but not as urgent as other concerns. in january 2006, the pew research center found 62 percent of the public said addressing medicare's financial problems should be a high priority for the government, but that still put it behind other priorities. surveys suggest that there's no public consensus behind any specific strategy to keep the program solvent. fraud and waste the government accountability office lists medicare as a "high-risk" government program in need of reform, in part because of its vulnerability to fraud and partly because of its long-term financial problems. fewer than 5% of medicare claims are audited. criticism robert m. ball, a former commissioner of social security under president kennedy in 1961 (and later under johnson, and nixon) defined the major obstacle to financing health insurance for the elderly: the high cost of care for the aged combined with the generally low incomes of retired people. because retired older people use much more medical care than younger employed people, an insurance premium related to the risk for older people needed to be high, but if the high premium had to be paid after retirement, when incomes are low, it was an almost impossible burden for the average person. the only feasible approach, he said, was to finance health insurance in the same way as cash benefits for retirement, by contributions paid while at work, when the payments are least burdensome, with the protection furnished in retirement without further payment. in the early 1960s relatively few of the elderly had health insurance, and what they had was usually inadequate. insurers such as blue cross, which had originally applied the principle of community rating, faced competition from other commercial insurers that did not community rate, and so were forced to raise their rates for the elderly. medicare is not generally an unearned entitlement. entitlement is most commonly based on a record of contributions to the medicare fund. as such it is a form of social insurance making it feasible for people to pay for insurance for sickness in old age when they are young and able to work and be assured of getting back benefits when they are older and no longer working. some people will pay in more than they receive back and others will receive more benefits than they paid in. unlike private insurance where some amount must be paid to attain coverage, all eligible persons can receive coverage regardless of how much or if they had ever paid in. politicized payment bruce vladeck, director of the health care financing administration in the clinton administration, has argued that lobbyists have changed the medicare program "from one that provides a legal entitlement to beneficiaries to one that provides a de facto political entitlement to providers." quality of beneficiary services a 2001 study by the government accountability office evaluated the quality of responses given by medicare contractor customer service representatives to provider (physician) questions. the evaluators assembled a list of questions, which they asked during a random sampling of calls to medicare contractors. the rate of complete, accurate information provided by medicare customer service representatives was 15%. since then, steps have been taken to improve the quality of customer service given by medicare contractors, specifically the 1-800-medicare contractor. as a result, 1-800-medicare customer service representatives (csr) have seen an increase in training, quality assurance monitoring has significantly increased, and a customer satisfaction survey is offered to random callers. hospital accreditation in most states the joint commission, a private, non-profit organization for accrediting hospitals, decides whether or not a hospital is able to participate in medicare, as currently there are no competitor organizations recognized by cms. other organizations can also accredit hospitals for medicare. these include the community health accreditation program, the accreditation commission for health care, the compliance team and the healthcare quality association on accreditation. accreditation is voluntary and an organization may choose to be evaluated by their state survey agency or by cms directly. graduate medical education medicare funds the vast majority of residency training in the us. this tax-based financing covers resident salaries and benefits through payments called direct medical education payments. medicare also uses taxes for indirect medical education, a subsidy paid to teaching hospitals in exchange for training resident physicians. for the 2008 fiscal year these payments were $2.7 billion and $5.7 billion, respectively. overall funding levels have remained at the same level since 1996, so that the same number or fewer residents have been trained under this program. meanwhile, the us population continues to grow both older and larger, which has led to greater demand for physicians, in part due to higher rates of illness and disease among the elderly compared to younger individuals. at the same time the cost of medical services continue rising rapidly and many geographic areas face physician shortages, both trends suggesting the supply of physicians remains too low. medicare thus finds itself in the odd position of having assumed control of the single largest funding source for graduate medical education, currently facing major budget constraints, and as a result, freezing funding for graduate medical education, as well as for physician reimbursement rates. this has forced hospitals to look for alternative sources of funding for residency slots. this halt in funding in turn exacerbates the exact problem medicare sought to solve in the first place: improving the availability of medical care. however, some healthcare administration experts believe that the shortage of physicians may be an opportunity for providers to reorganize