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单选题Disability among the elderly has declined markedly in the United States in the past two decades. In 1984, 25 percent of the elderly population reported difficulty with activities associated with independent living. By 1999, the share had fallen to 20 percent, a decline of one-fifth. Although these basic facts are well known, their interpretation is not clear. Is the reduction in disability a result of improved medical care, individual behavioral changes, environmental modifications that allow the elderly to better function by themselves, or other demographic changes? Will the trend continue, or is it time limited? What does the reduction in disability mean for years of healthy life and labor force participation? The researchers David Cutler, Mary Beth Landrum, and Kate Stewart focus on disability caused by cardiovascular disease to investigate the role of improved medical care on reductions in disability. By looking at just one condition, they can analyze health shocks and their outcomes in some detail. Cardiovascular disease is a natural condition to analyze, because it is the most common cause of death in the United States and most other developed countries. Also, more is spent on cardiovascular disease than on any other condition, clearly a case where medical care could really matter. The researchers measure disability as the presence of impairments in. Activities of Daily Living (ADLs) and Instrumental Activities of Daily Living (IADLs). Their data source, the National Long-Term Care Survey(NLTCS) , includes information on six ADL measures: eating, getting in or out of bed, walking around inside, dressing, bathing, and getting to or using the toilet. There are also questions about eight IADL measures: doing light housework or laundry, preparing meals, shopping for groceries, getting around outside, managing money, taking medications, and making telephone calls. The NLTCS is a nationally representative longitudinal survey of the health and disability profile of the population aged 65 and over. Cutler and his co-researchers find that reduced disability associated with cardiovascular disease accounts for a significant part of the total reduction in disability--between 14 and 22 percent. The evidence suggests that improvements in medical care, including both increased use of relevant procedures and pharmaceuticals, led to a significant part of this decline in disability. Regions with higher use experienced substantial reductions in mortality and disability. While precise data on the implications of reduced disability are lacking, the possible impact of disability reductions is staggering. The researchers estimate that preventing disability after an acute cardiovascular event can add as much as 3.7 years of quality-adjusted life expectancy, or perhaps $ 316,000 of value. The cost of this outcome is significantly smaller. The initial treatment costs range from $ 8,610 to $ 16,332, depending on the procedure used. Further, recent cost analyses reported that annual Medicare spending was lower for the non-disabled than the disabled, which suggests that higher treatment costs may be offset by lower future spending among a more healthy population. By virtually any measure, therefore, the researchers conclude that medical technology after acute cardiovascular episodes is worth the cost.

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单选题曲线y=x2与直线x=0，x=1，y=t(0＜t＜1)所围的图形的面积为( )．

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单选题函数z=x 2 -xy+y 2 +9x-6y+20有______

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单选题设函数，则f(x)的间断点______

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单选题设函数f(x)在(-∞，+∞)内有定义，且f(x)的反函数为g(x)．记则

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