| 年份 | 美国  | 
                                                            
|---|---|
| 2023 | - | 
| 2022 | - | 
| 2021 | 0.101999 | 
| 2020 | 0.0213895 | 
| 2019 | 0.0187501 | 
| 2018 | 0.0352448 | 
| 2017 | 0.0412677 | 
| 2016 | 0.0380022 | 
| 2015 | 0.0362503 | 
| 2014 | 0.0880467 | 
| 2013 | 0.120357 | 
| 2012 | 0.163415 | 
| 2011 | 0.238997 | 
| 2010 | 0.166896 | 
| 2009 | 0.0738567 | 
| 2008 | 0.110497 | 
| 2007 | 0.0700163 | 
| 2006 | 0.0637465 | 
| 2005 | 0.0256054 | 
| 2004 | 0.0190643 | 
| 2003 | 0.010402 | 
| 2002 | 0.00516846 | 
| 2001 | 0.0077513 | 
| 2000 | 0.0134401 | 
| 1999 | 0.0206751 | 
| 1998 | 0.0250267 | 
| 1997 | 0.0352191 | 
| 1996 | 0.0425169 | 
| 1995 | 0.059767 | 
| 1994 | 0.0491397 | 
| 1993 | 0.036019 | 
| 1992 | 0.0399068 | 
| 1991 | 0.0284623 | 
| 1990 | 0.0478146 | 
| 1989 | 0.0529651 | 
| 1988 | 0.106855 | 
| 1987 | 0.033825 | 
| 1986 | 0.022162 | 
| 1985 | 0.0325718 | 
| 1984 | 0.0303192 | 
| 1983 | 0.0502391 | 
| 1982 | 0.0469297 | 
| 1981 | 0.091113 | 
| 1980 | 0.121598 | 
| 1979 | 0.109963 | 
| 1978 | 0.064932 | 
| 1977 | 0.152848 | 
| 1976 | 0.116862 | 
| 1975 | 0.191622 | 
| 1974 | 0.284318 | 
| 1973 | 0.174314 | 
| 1972 | 0.0903275 | 
| 1971 | 0.0981639 | 
| 1970 | 0.173695 | 
| 1969 | - | 
| 1968 | - | 
| 1967 | - | 
| 1966 | - | 
| 1965 | - | 
| 1964 | - | 
| 1963 | - | 
| 1962 | - | 
| 1961 | - | 
| 1960 | - |