| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 0.295165 |
| 2020 | 0.295165 |
| 2019 | 0.295165 |
| 2018 | 0.295165 |
| 2017 | 0.295165 |
| 2016 | 0.295165 |
| 2015 | 0.295165 |
| 2014 | 0.295165 |
| 2013 | 0.295165 |
| 2012 | 0.295165 |
| 2011 | 0.295165 |
| 2010 | 0.295165 |
| 2009 | 0.295165 |
| 2008 | 0.295165 |
| 2007 | 0.294698 |
| 2006 | 0.294698 |
| 2005 | 0.294698 |
| 2004 | 0.294698 |
| 2003 | 0.297972 |
| 2002 | 0.297972 |
| 2001 | 0.294698 |
| 2000 | 0.294698 |
| 1999 | 0.294793 |
| 1998 | 0.272957 |
| 1997 | 0.272957 |
| 1996 | 0.25112 |
| 1995 | 0.25112 |
| 1994 | 0.240202 |
| 1993 | 0.240202 |
| 1992 | 0.229284 |
| 1991 | 0.229284 |
| 1990 | 0.229284 |
| 1989 | 0.223825 |
| 1988 | 0.222078 |
| 1987 | 0.222078 |
| 1986 | 0.222078 |
| 1985 | 0.222078 |
| 1984 | 0.222078 |
| 1983 | 0.222078 |
| 1982 | 0.222078 |
| 1981 | 0.204062 |
| 1980 | 0.204062 |
| 1979 | 0.204062 |
| 1978 | 0.204062 |
| 1977 | 0.190087 |
| 1976 | 0.190633 |
| 1975 | 0.190633 |
| 1974 | 0.190633 |
| 1973 | 0.19107 |
| 1972 | 0.191616 |
| 1971 | 0.192162 |
| 1970 | 0.192707 |
| 1969 | 0.193253 |
| 1968 | 0.195983 |
| 1967 | 0.198713 |
| 1966 | 0.201442 |
| 1965 | 0.204499 |
| 1964 | 0.204499 |
| 1963 | 0.204062 |
| 1962 | 0.20701 |
| 1961 | 0.205154 |
| 1960 | - |