| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 1.664 |
| 2020 | 1.6415 |
| 2019 | 1.706 |
| 2018 | 1.7295 |
| 2017 | 1.7655 |
| 2016 | 1.8205 |
| 2015 | 1.8435 |
| 2014 | 1.8625 |
| 2013 | 1.8575 |
| 2012 | 1.8805 |
| 2011 | 1.8945 |
| 2010 | 1.931 |
| 2009 | 2.002 |
| 2008 | 2.072 |
| 2007 | 2.12 |
| 2006 | 2.108 |
| 2005 | 2.057 |
| 2004 | 2.0515 |
| 2003 | 2.0475 |
| 2002 | 2.0205 |
| 2001 | 2.0305 |
| 2000 | 2.056 |
| 1999 | 2.0075 |
| 1998 | 1.999 |
| 1997 | 1.971 |
| 1996 | 1.976 |
| 1995 | 1.978 |
| 1994 | 2.0015 |
| 1993 | 2.0195 |
| 1992 | 2.046 |
| 1991 | 2.0625 |
| 1990 | 2.081 |
| 1989 | 2.014 |
| 1988 | 1.934 |
| 1987 | 1.872 |
| 1986 | 1.8375 |
| 1985 | 1.844 |
| 1984 | 1.8065 |
| 1983 | 1.799 |
| 1982 | 1.8275 |
| 1981 | 1.812 |
| 1980 | 1.8395 |
| 1979 | 1.808 |
| 1978 | 1.76 |
| 1977 | 1.79 |
| 1976 | 1.738 |
| 1975 | 1.774 |
| 1974 | 1.835 |
| 1973 | 1.879 |
| 1972 | 2.01 |
| 1971 | 2.266 |
| 1970 | 2.48 |
| 1969 | 2.456 |
| 1968 | 2.464 |
| 1967 | 2.558 |
| 1966 | 2.721 |
| 1965 | 2.913 |
| 1964 | 3.19 |
| 1963 | 3.319 |
| 1962 | 3.461 |
| 1961 | 3.62 |
| 1960 | 3.654 |