| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | - |
| 2021 | 73.5 |
| 2020 | 74.2 |
| 2019 | 76.3 |
| 2018 | 76.2 |
| 2017 | 76.1 |
| 2016 | 76.1 |
| 2015 | 76.3 |
| 2014 | 76.5 |
| 2013 | 76.4 |
| 2012 | 76.4 |
| 2011 | 76.3 |
| 2010 | 76.2 |
| 2009 | 76 |
| 2008 | 75.6 |
| 2007 | 75.5 |
| 2006 | 75.2 |
| 2005 | 75 |
| 2004 | 75 |
| 2003 | 74.5 |
| 2002 | 74.4 |
| 2001 | 74.3 |
| 2000 | 74.1 |
| 1999 | 73.9 |
| 1998 | 73.8 |
| 1997 | 73.6 |
| 1996 | 73.1 |
| 1995 | 72.5 |
| 1994 | 72.4 |
| 1993 | 72.2 |
| 1992 | 72.3 |
| 1991 | 72 |
| 1990 | 71.8 |
| 1989 | 71.7 |
| 1988 | 71.4 |
| 1987 | 71.4 |
| 1986 | 71.2 |
| 1985 | 71.1 |
| 1984 | 71.1 |
| 1983 | 71 |
| 1982 | 70.8 |
| 1981 | 70.4 |
| 1980 | 70 |
| 1979 | 70 |
| 1978 | 69.6 |
| 1977 | 69.5 |
| 1976 | 69.1 |
| 1975 | 68.8 |
| 1974 | 68.2 |
| 1973 | 67.6 |
| 1972 | 67.4 |
| 1971 | 67.4 |
| 1970 | 67.1 |
| 1969 | 66.8 |
| 1968 | 66 |
| 1967 | 67 |
| 1966 | 66.7 |
| 1965 | 66.8 |
| 1964 | 66.8 |
| 1963 | 66.6 |
| 1962 | 66.9 |
| 1961 | 67.1 |
| 1960 | 66.6 |