| 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 |