| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | 3.21117 |
| 2021 | 3.1273 |
| 2020 | 3.06385 |
| 2019 | 3.02381 |
| 2018 | 3.00597 |
| 2017 | 2.99961 |
| 2016 | 2.98529 |
| 2015 | 2.9703 |
| 2014 | 2.976 |
| 2013 | 2.95249 |
| 2012 | 2.91481 |
| 2011 | 2.86507 |
| 2010 | 2.77943 |
| 2009 | 2.65585 |
| 2008 | 2.53549 |
| 2007 | 2.44605 |
| 2006 | 2.35699 |
| 2005 | 2.30172 |
| 2004 | 2.27379 |
| 2003 | 2.20073 |
| 2002 | 2.12712 |
| 2001 | 2.0876 |
| 2000 | 2.03808 |
| 1999 | 1.98537 |
| 1998 | 1.95103 |
| 1997 | 1.93965 |
| 1996 | 1.92092 |
| 1995 | 1.89791 |
| 1994 | 1.8742 |
| 1993 | 1.84742 |
| 1992 | 1.81526 |
| 1991 | 1.77158 |
| 1990 | 1.7321 |
| 1989 | 1.70168 |
| 1988 | 1.67263 |
| 1987 | 1.63954 |
| 1986 | 1.61278 |
| 1985 | 1.5892 |
| 1984 | 1.56538 |
| 1983 | 1.55702 |
| 1982 | 1.53393 |
| 1981 | 1.5095 |
| 1980 | 1.50192 |
| 1979 | 1.49283 |
| 1978 | 1.47858 |
| 1977 | 1.45736 |
| 1976 | 1.43854 |
| 1975 | 1.41408 |
| 1974 | 1.38848 |
| 1973 | 1.37839 |
| 1972 | 1.37643 |
| 1971 | 1.36789 |
| 1970 | 1.35448 |
| 1969 | 1.33559 |
| 1968 | 1.31069 |
| 1967 | 1.28772 |
| 1966 | 1.26894 |
| 1965 | 1.24877 |
| 1964 | 1.22531 |
| 1963 | 1.20741 |
| 1962 | 1.19437 |
| 1961 | 1.17934 |
| 1960 | 1.16349 |