| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 10.8927 |
| 2020 | 10.2021 |
| 2019 | 11.8725 |
| 2018 | 12.361 |
| 2017 | 12.2617 |
| 2016 | 11.9395 |
| 2015 | 12.461 |
| 2014 | 13.546 |
| 2013 | 13.5781 |
| 2012 | 13.644 |
| 2011 | 13.5635 |
| 2010 | 12.3414 |
| 2009 | 10.9322 |
| 2008 | 12.4258 |
| 2007 | 11.4638 |
| 2006 | 10.6414 |
| 2005 | 9.98205 |
| 2004 | 9.62875 |
| 2003 | 9.03566 |
| 2002 | 9.13138 |
| 2001 | 9.70345 |
| 2000 | 10.6928 |
| 1999 | 10.3093 |
| 1998 | 10.5153 |
| 1997 | 11.1198 |
| 1996 | 10.7466 |
| 1995 | 10.6392 |
| 1994 | 9.89315 |
| 1993 | 9.54718 |
| 1992 | 9.70891 |
| 1991 | 9.6609 |
| 1990 | 9.25473 |
| 1989 | 8.93879 |
| 1988 | 8.49052 |
| 1987 | 7.49592 |
| 1986 | 7.00925 |
| 1985 | 6.98807 |
| 1984 | 7.48908 |
| 1983 | 7.62226 |
| 1982 | 8.46973 |
| 1981 | 9.51778 |
| 1980 | 9.82646 |
| 1979 | 8.75903 |
| 1978 | 7.94706 |
| 1977 | 7.65429 |
| 1976 | 7.98089 |
| 1975 | 8.23228 |
| 1974 | 8.19612 |
| 1973 | 6.68378 |
| 1972 | 5.53846 |
| 1971 | 5.40525 |
| 1970 | 5.56311 |
| 1969 | - |
| 1968 | - |
| 1967 | - |
| 1966 | - |
| 1965 | - |
| 1964 | - |
| 1963 | - |
| 1962 | - |
| 1961 | - |
| 1960 | - |