| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 14.3844 |
| 2020 | 14.9017 |
| 2019 | 14.0722 |
| 2018 | 13.9625 |
| 2017 | 13.9986 |
| 2016 | 14.2449 |
| 2015 | 14.3303 |
| 2014 | 14.622 |
| 2013 | 15.0366 |
| 2012 | 15.4758 |
| 2011 | 16.0984 |
| 2010 | 16.6858 |
| 2009 | 16.8077 |
| 2008 | 15.9341 |
| 2007 | 15.1893 |
| 2006 | 15.0045 |
| 2005 | 15.0471 |
| 2004 | 15.1583 |
| 2003 | 15.2436 |
| 2002 | 15.059 |
| 2001 | 14.5356 |
| 2000 | 14.024 |
| 1999 | 14.0318 |
| 1998 | 13.9869 |
| 1997 | 14.2293 |
| 1996 | 14.5283 |
| 1995 | 14.9448 |
| 1994 | 15.2061 |
| 1993 | 15.6453 |
| 1992 | 16.0787 |
| 1991 | 16.3176 |
| 1990 | 15.9008 |
| 1989 | 15.6238 |
| 1988 | 15.6682 |
| 1987 | 16.0012 |
| 1986 | 16.1146 |
| 1985 | 15.9171 |
| 1984 | 15.7204 |
| 1983 | 16.3838 |
| 1982 | 16.5839 |
| 1981 | 15.8102 |
| 1980 | 15.8768 |
| 1979 | 15.4036 |
| 1978 | 15.7667 |
| 1977 | 16.388 |
| 1976 | 16.788 |
| 1975 | 17.6108 |
| 1974 | 17.1627 |
| 1973 | 16.7763 |
| 1972 | 17.6293 |
| 1971 | 17.9388 |
| 1970 | 17.9618 |
| 1969 | - |
| 1968 | - |
| 1967 | - |
| 1966 | - |
| 1965 | - |
| 1964 | - |
| 1963 | - |
| 1962 | - |
| 1961 | - |
| 1960 | - |