| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | 12.3236 |
| 2021 | 11.4356 |
| 2020 | 10.3385 |
| 2019 | 9.95934 |
| 2018 | 9.98924 |
| 2017 | 11.5835 |
| 2016 | 10.9183 |
| 2015 | 11.2375 |
| 2014 | 10.9354 |
| 2013 | 10.4835 |
| 2012 | 9.76392 |
| 2011 | 9.53893 |
| 2010 | 8.56323 |
| 2009 | 7.90352 |
| 2008 | 10.2762 |
| 2007 | 11.2899 |
| 2006 | 11.3105 |
| 2005 | 10.6817 |
| 2004 | 9.53747 |
| 2003 | 9.3907 |
| 2002 | 9.86801 |
| 2001 | 11.8577 |
| 2000 | 12.9708 |
| 1999 | 12.26 |
| 1998 | 12.3298 |
| 1997 | 11.8282 |
| 1996 | 11.3739 |
| 1995 | 10.981 |
| 1994 | 10.6235 |
| 1993 | 10.3049 |
| 1992 | 9.98416 |
| 1991 | 10.3203 |
| 1990 | 10.4653 |
| 1989 | 10.7824 |
| 1988 | 10.5959 |
| 1987 | 10.9488 |
| 1986 | 10.163 |
| 1985 | 10.3842 |
| 1984 | 10.1597 |
| 1983 | 10.3483 |
| 1982 | 11.9786 |
| 1981 | 12.5505 |
| 1980 | 12.1384 |
| 1979 | 12.0038 |
| 1978 | 11.5424 |
| 1977 | 11.6186 |
| 1976 | 10.7488 |
| 1975 | 11.1858 |
| 1974 | 11.8376 |
| 1973 | 11.4952 |
| 1972 | 11.8199 |
| 1971 | - |
| 1970 | - |
| 1969 | - |
| 1968 | - |
| 1967 | - |
| 1966 | - |
| 1965 | - |
| 1964 | - |
| 1963 | - |
| 1962 | - |
| 1961 | - |
| 1960 | - |