| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | 2.91013 |
| 2021 | 2.71167 |
| 2020 | 2.57217 |
| 2019 | 2.52678 |
| 2018 | 2.44264 |
| 2017 | 2.34575 |
| 2016 | 2.30744 |
| 2015 | 2.27609 |
| 2014 | 2.21627 |
| 2013 | 2.19451 |
| 2012 | 2.19958 |
| 2011 | 2.20255 |
| 2010 | 2.23152 |
| 2009 | 2.31889 |
| 2008 | 2.37295 |
| 2007 | 2.38904 |
| 2006 | 2.40113 |
| 2005 | 2.35431 |
| 2004 | 2.24891 |
| 2003 | 2.19888 |
| 2002 | 2.1928 |
| 2001 | 2.14536 |
| 2000 | 2.14361 |
| 1999 | 2.19718 |
| 1998 | 2.16747 |
| 1997 | 2.09059 |
| 1996 | 2.06683 |
| 1995 | 2.03099 |
| 1994 | 1.96994 |
| 1993 | 1.94035 |
| 1992 | 1.95655 |
| 1991 | 1.9618 |
| 1990 | 1.95393 |
| 1989 | 1.94308 |
| 1988 | 1.92734 |
| 1987 | 1.90412 |
| 1986 | 1.85662 |
| 1985 | 1.81453 |
| 1984 | 1.78928 |
| 1983 | 1.74663 |
| 1982 | 1.71297 |
| 1981 | 1.6934 |
| 1980 | 1.66077 |
| 1979 | 1.63151 |
| 1978 | 1.62571 |
| 1977 | 1.60554 |
| 1976 | 1.58248 |
| 1975 | 1.58438 |
| 1974 | 1.58406 |
| 1973 | 1.5704 |
| 1972 | 1.55153 |
| 1971 | 1.5438 |
| 1970 | 1.54244 |
| 1969 | 1.54672 |
| 1968 | 1.56518 |
| 1967 | 1.58732 |
| 1966 | 1.58808 |
| 1965 | 1.57697 |
| 1964 | 1.57119 |
| 1963 | 1.56671 |
| 1962 | 1.56213 |
| 1961 | 1.55372 |
| 1960 | 1.53784 |