| 年份 | 美国  | 
                                                            
|---|---|
| 2023 | - | 
| 2022 | - | 
| 2021 | 0.165542 | 
| 2020 | 0.083695 | 
| 2019 | 0.131587 | 
| 2018 | 0.19837 | 
| 2017 | 0.182333 | 
| 2016 | 0.135997 | 
| 2015 | 0.15481 | 
| 2014 | 0.226671 | 
| 2013 | 0.279719 | 
| 2012 | 0.365038 | 
| 2011 | 0.576151 | 
| 2010 | 0.463272 | 
| 2009 | 0.328948 | 
| 2008 | 0.69688 | 
| 2007 | 0.249876 | 
| 2006 | 0.275792 | 
| 2005 | 0.265072 | 
| 2004 | 0.321325 | 
| 2003 | 0.154156 | 
| 2002 | 0.151822 | 
| 2001 | 0.212622 | 
| 2000 | 0.140193 | 
| 1999 | 0.127171 | 
| 1998 | 0.162197 | 
| 1997 | 0.182766 | 
| 1996 | 0.196221 | 
| 1995 | 0.185739 | 
| 1994 | 0.0632599 | 
| 1993 | 0.0657599 | 
| 1992 | 0.137242 | 
| 1991 | 0.175651 | 
| 1990 | 0.195194 | 
| 1989 | 0.181418 | 
| 1988 | 0.140726 | 
| 1987 | 0.107592 | 
| 1986 | 0.199445 | 
| 1985 | 0.305577 | 
| 1984 | 0.307097 | 
| 1983 | 0.384582 | 
| 1982 | 0.741094 | 
| 1981 | 0.71839 | 
| 1980 | 0.533324 | 
| 1979 | 0.413817 | 
| 1978 | 0.402225 | 
| 1977 | 0.546537 | 
| 1976 | 0.582522 | 
| 1975 | 0.574744 | 
| 1974 | 0.247654 | 
| 1973 | 0.121739 | 
| 1972 | 0.109536 | 
| 1971 | 0.103469 | 
| 1970 | 0.0930505 | 
| 1969 | - | 
| 1968 | - | 
| 1967 | - | 
| 1966 | - | 
| 1965 | - | 
| 1964 | - | 
| 1963 | - | 
| 1962 | - | 
| 1961 | - | 
| 1960 | - |