Canada, France, Germany, Italy, Japan, Spain, and the United Kingdom). The United States ranked at the top of this group of countries in 1950 but dropped to last place in 2006 (United Nations, 2011).

Why does the United States now rank so low in international life expectancy comparisons? This question has drawn the attention and concern of researchers and policy makers. The current situation is especially surprising given that the United States spends far more on health care than any other country. In response to these concerns, the National Research Council (NRC) appointed a committee of experts in 2008 to investigate the reasons for this divergence between the United States and other high-income countries. In its final report the committee reached several conclusions (National Research Council, 2011):

A history of heavy smoking and current levels of obesity are playing a substantial role in the relatively poor longevity performance of the United States. (p. S-4)

The damage caused by smoking was estimated to account for 78 percent of the gap in life expectancy for women and 41 percent of the gap for men between the United States and other high income countries in 2003. (p. S-2)

Obesity may account for a fifth to a third of the shortfall of life expectancy in the United States relative to the other countries studied. (p. S-2)

What are the implications of these conclusions for future trends in life expectancy? Mortality will likely continue to decline as further progress is made in medicine, biotechnology, public health, nutrition, access to medical services, incomes, and education. However, substantial disagreement exists among analysts about how rapidly future improvements will occur (Bongaarts, 2006; Wilmoth, 1997 and 2001). At one end of the spectrum of opinion are pessimists (Carnes, Olshansky, and Grahn, 1996; Olshansky et al., 2005), who believe that the most advanced countries are close to a biological limit to longevity. A very different opinion is held by optimists (Oeppen and Vaupel, 2002), who expect life expectancy at birth to continue to rise very rapidly, reaching over 100 years later this century. Most projections by researchers and government agencies fall between these extremes (Lee and Carter, 1992; Li and Lee, 2005; Tuljapurkar, Li, and Boe, 2000; Bongaarts, 2006). The best-known U.S. projection is the one used by the Social Security Administration. The 2011 Report of the Board of Trustees of the Federal Old-Age and Survivors Insurance and Federal Disability Insurance Trust Funds (commonly known as the Trustees Report) projects life expectancy to reach 82.2 years in 2050, up from 77.7 in 2006.

In 2010 the Social Security Advisory Board appointed the Technical Panel on Assumptions and Methods (TPAM) to assess the assumptions and methods used in the Trustees Report. The TPAM made a number of



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