| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 14.5887 |
| 2020 | 13.1816 |
| 2019 | 14.5795 |
| 2018 | 15.2494 |
| 2017 | 15.0174 |
| 2016 | 14.6475 |
| 2015 | 15.3512 |
| 2014 | 16.452 |
| 2013 | 16.4243 |
| 2012 | 17.0378 |
| 2011 | 17.279 |
| 2010 | 15.8785 |
| 2009 | 13.8273 |
| 2008 | 17.4419 |
| 2007 | 16.5482 |
| 2006 | 16.3339 |
| 2005 | 15.6565 |
| 2004 | 14.8193 |
| 2003 | 13.5917 |
| 2002 | 13.155 |
| 2001 | 13.2637 |
| 2000 | 14.4102 |
| 1999 | 13.0042 |
| 1998 | 12.3106 |
| 1997 | 12.3086 |
| 1996 | 11.9404 |
| 1995 | 11.8142 |
| 1994 | 11.1623 |
| 1993 | 10.4974 |
| 1992 | 10.2417 |
| 1991 | 10.1255 |
| 1990 | 10.5603 |
| 1989 | 10.4763 |
| 1988 | 10.5796 |
| 1987 | 10.4777 |
| 1986 | 9.88872 |
| 1985 | 9.61583 |
| 1984 | 10.0333 |
| 1983 | 9.04333 |
| 1982 | 9.06708 |
| 1981 | 9.90814 |
| 1980 | 10.2834 |
| 1979 | 9.61713 |
| 1978 | 9.02577 |
| 1977 | 8.76361 |
| 1976 | 8.06795 |
| 1975 | 7.28409 |
| 1974 | 8.24886 |
| 1973 | 6.39544 |
| 1972 | 5.80216 |
| 1971 | 5.35193 |
| 1970 | 5.19518 |
| 1969 | - |
| 1968 | - |
| 1967 | - |
| 1966 | - |
| 1965 | - |
| 1964 | - |
| 1963 | - |
| 1962 | - |
| 1961 | - |
| 1960 | - |