| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | 5.77207 |
| 2021 | 5.86905 |
| 2020 | 5.99625 |
| 2019 | 6.1245 |
| 2018 | 6.2228 |
| 2017 | 6.29465 |
| 2016 | 6.35087 |
| 2015 | 6.40598 |
| 2014 | 6.46851 |
| 2013 | 6.54569 |
| 2012 | 6.635 |
| 2011 | 6.71557 |
| 2010 | 6.78997 |
| 2009 | 6.86945 |
| 2008 | 6.9332 |
| 2007 | 6.96504 |
| 2006 | 6.98884 |
| 2005 | 7.02546 |
| 2004 | 7.0525 |
| 2003 | 7.05958 |
| 2002 | 7.06532 |
| 2001 | 7.08505 |
| 2000 | 7.12576 |
| 1999 | 7.19042 |
| 1998 | 7.28078 |
| 1997 | 7.40105 |
| 1996 | 7.55139 |
| 1995 | 7.70877 |
| 1994 | 7.83265 |
| 1993 | 7.89472 |
| 1992 | 7.90084 |
| 1991 | 7.87644 |
| 1990 | 7.83698 |
| 1989 | 7.78247 |
| 1988 | 7.73071 |
| 1987 | 7.70861 |
| 1986 | 7.71416 |
| 1985 | 7.73411 |
| 1984 | 7.75393 |
| 1983 | 7.75547 |
| 1982 | 7.71679 |
| 1981 | 7.63047 |
| 1980 | 7.52968 |
| 1979 | 7.44614 |
| 1978 | 7.38818 |
| 1977 | 7.38596 |
| 1976 | 7.50708 |
| 1975 | 7.74821 |
| 1974 | 8.00955 |
| 1973 | 8.24244 |
| 1972 | 8.44647 |
| 1971 | 8.6059 |
| 1970 | 8.75351 |
| 1969 | 8.98281 |
| 1968 | 9.3271 |
| 1967 | 9.73174 |
| 1966 | 10.1412 |
| 1965 | 10.5136 |
| 1964 | 10.813 |
| 1963 | 11.0467 |
| 1962 | 11.2469 |
| 1961 | 11.4028 |
| 1960 | 11.4967 |