| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 25.4814 |
| 2020 | 23.3838 |
| 2019 | 26.452 |
| 2018 | 27.6104 |
| 2017 | 27.2792 |
| 2016 | 26.587 |
| 2015 | 27.8122 |
| 2014 | 29.998 |
| 2013 | 30.0024 |
| 2012 | 30.6818 |
| 2011 | 30.8425 |
| 2010 | 28.2199 |
| 2009 | 24.7595 |
| 2008 | 29.8678 |
| 2007 | 28.012 |
| 2006 | 26.9753 |
| 2005 | 25.6386 |
| 2004 | 24.4481 |
| 2003 | 22.6273 |
| 2002 | 22.2864 |
| 2001 | 22.9672 |
| 2000 | 25.103 |
| 1999 | 23.3136 |
| 1998 | 22.8259 |
| 1997 | 23.4283 |
| 1996 | 22.6871 |
| 1995 | 22.4534 |
| 1994 | 21.0555 |
| 1993 | 20.0446 |
| 1992 | 19.9506 |
| 1991 | 19.7864 |
| 1990 | 19.8151 |
| 1989 | 19.4151 |
| 1988 | 19.0701 |
| 1987 | 17.9736 |
| 1986 | 16.898 |
| 1985 | 16.6039 |
| 1984 | 17.5224 |
| 1983 | 16.6656 |
| 1982 | 17.5368 |
| 1981 | 19.4259 |
| 1980 | 20.1098 |
| 1979 | 18.3762 |
| 1978 | 16.9728 |
| 1977 | 16.4179 |
| 1976 | 16.0488 |
| 1975 | 15.5164 |
| 1974 | 16.445 |
| 1973 | 13.0792 |
| 1972 | 11.3406 |
| 1971 | 10.7572 |
| 1970 | 10.7583 |
| 1969 | - |
| 1968 | - |
| 1967 | - |
| 1966 | - |
| 1965 | - |
| 1964 | - |
| 1963 | - |
| 1962 | - |
| 1961 | - |
| 1960 | - |