| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 0.0377125 |
| 2020 | 0.0367964 |
| 2019 | 0.0382161 |
| 2018 | 0.0346275 |
| 2017 | 0.0414197 |
| 2016 | 0.0370311 |
| 2015 | 0.0357864 |
| 2014 | 0.0438896 |
| 2013 | 0.0451078 |
| 2012 | 0.0423162 |
| 2011 | 0.0490358 |
| 2010 | 0.0447732 |
| 2009 | 0.0364101 |
| 2008 | 0.048725 |
| 2007 | 0.0619743 |
| 2006 | 0.0591478 |
| 2005 | 0.0579062 |
| 2004 | 0.0606211 |
| 2003 | 0.0567834 |
| 2002 | 0.0566642 |
| 2001 | 0.0591206 |
| 2000 | 0.0726288 |
| 1999 | 0.0773646 |
| 1998 | 0.0749014 |
| 1997 | 0.102146 |
| 1996 | 0.107446 |
| 1995 | 0.117525 |
| 1994 | 0.116395 |
| 1993 | 0.134982 |
| 1992 | 0.10188 |
| 1991 | 0.101774 |
| 1990 | 0.125225 |
| 1989 | 0.113603 |
| 1988 | 0.110941 |
| 1987 | 0.108795 |
| 1986 | 0.103213 |
| 1985 | 0.0872045 |
| 1984 | 0.101098 |
| 1983 | 0.106904 |
| 1982 | 0.126036 |
| 1981 | 0.117361 |
| 1980 | 0.150946 |
| 1979 | 0.182518 |
| 1978 | 0.171732 |
| 1977 | 0.15328 |
| 1976 | 0.151764 |
| 1975 | 0.159836 |
| 1974 | 0.147975 |
| 1973 | 0.15769 |
| 1972 | 0.120869 |
| 1971 | 0.129652 |
| 1970 | 0.108947 |
| 1969 | - |
| 1968 | - |
| 1967 | - |
| 1966 | - |
| 1965 | - |
| 1964 | - |
| 1963 | - |
| 1962 | - |
| 1961 | - |
| 1960 | - |