| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 0.611483 |
| 2020 | 0.187625 |
| 2019 | 0.368545 |
| 2018 | 0.319248 |
| 2017 | 0.162526 |
| 2016 | 0.0922955 |
| 2015 | 0.00752518 |
| 2014 | 0.292227 |
| 2013 | 0.30565 |
| 2012 | 0.205926 |
| 2011 | 0.370845 |
| 2010 | 0.293763 |
| 2009 | 0.25964 |
| 2008 | 0.521499 |
| 2007 | 0.356898 |
| 2006 | 0.349464 |
| 2005 | 0.350823 |
| 2004 | 0.283171 |
| 2003 | 0.211789 |
| 2002 | 0.172817 |
| 2001 | 0.169433 |
| 2000 | 0.307551 |
| 1999 | 0.164265 |
| 1998 | 0.0755585 |
| 1997 | 0.203604 |
| 1996 | 0.351312 |
| 1995 | 0.295557 |
| 1994 | 0.292003 |
| 1993 | 0.348054 |
| 1992 | 0.441873 |
| 1991 | 0.477259 |
| 1990 | 0.703237 |
| 1989 | 0.539634 |
| 1988 | 0.431204 |
| 1987 | 0.690239 |
| 1986 | 0.485561 |
| 1985 | 1.20811 |
| 1984 | 1.28028 |
| 1983 | 1.54216 |
| 1982 | 1.29087 |
| 1981 | 2.11596 |
| 1980 | 3.14542 |
| 1979 | 2.51516 |
| 1978 | 1.41342 |
| 1977 | 1.48213 |
| 1976 | 1.45989 |
| 1975 | 1.46934 |
| 1974 | 1.57099 |
| 1973 | 0.349942 |
| 1972 | 0.363639 |
| 1971 | 0.333819 |
| 1970 | 0.279989 |
| 1969 | - |
| 1968 | - |
| 1967 | - |
| 1966 | - |
| 1965 | - |
| 1964 | - |
| 1963 | - |
| 1962 | - |
| 1961 | - |
| 1960 | - |