| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 1.27994 |
| 2020 | 0.329506 |
| 2019 | 0.557098 |
| 2018 | 0.595679 |
| 2017 | 0.427546 |
| 2016 | 0.303325 |
| 2015 | 0.234372 |
| 2014 | 0.703154 |
| 2013 | 0.750834 |
| 2012 | 0.776694 |
| 2011 | 1.23503 |
| 2010 | 0.968704 |
| 2009 | 0.743921 |
| 2008 | 1.92914 |
| 2007 | 1.07811 |
| 2006 | 1.13066 |
| 2005 | 1.49664 |
| 2004 | 1.25369 |
| 2003 | 1.04592 |
| 2002 | 0.689227 |
| 2001 | 0.915678 |
| 2000 | 1.11329 |
| 1999 | 0.642859 |
| 1998 | 0.548987 |
| 1997 | 0.845706 |
| 1996 | 0.999136 |
| 1995 | 0.81517 |
| 1994 | 0.761583 |
| 1993 | 0.892085 |
| 1992 | 0.935695 |
| 1991 | 0.908449 |
| 1990 | 1.23251 |
| 1989 | 1.07194 |
| 1988 | 0.968882 |
| 1987 | 1.21731 |
| 1986 | 0.91013 |
| 1985 | 2.09298 |
| 1984 | 2.33921 |
| 1983 | 2.6667 |
| 1982 | 2.39193 |
| 1981 | 4.04888 |
| 1980 | 5.6815 |
| 1979 | 5.04457 |
| 1978 | 2.72849 |
| 1977 | 3.11412 |
| 1976 | 3.09035 |
| 1975 | 3.23053 |
| 1974 | 3.2762 |
| 1973 | 0.911328 |
| 1972 | 0.729816 |
| 1971 | 0.667662 |
| 1970 | 0.655681 |
| 1969 | - |
| 1968 | - |
| 1967 | - |
| 1966 | - |
| 1965 | - |
| 1964 | - |
| 1963 | - |
| 1962 | - |
| 1961 | - |
| 1960 | - |