| 年份 | 美国 |
|---|---|
| 2023 | - |
| 2022 | 0.377565 |
| 2021 | 0.156747 |
| 2020 | 0.964348 |
| 2019 | 0.455381 |
| 2018 | 0.526435 |
| 2017 | 0.632644 |
| 2016 | 0.724676 |
| 2015 | 0.736217 |
| 2014 | 0.733362 |
| 2013 | 0.69286 |
| 2012 | 0.7336 |
| 2011 | 0.726787 |
| 2010 | 0.829617 |
| 2009 | 0.876651 |
| 2008 | 0.945865 |
| 2007 | 0.951055 |
| 2006 | 0.964254 |
| 2005 | 0.921713 |
| 2004 | 0.925484 |
| 2003 | 0.859482 |
| 2002 | 0.927797 |
| 2001 | 0.989741 |
| 2000 | 1.11277 |
| 1999 | 1.14834 |
| 1998 | 1.16571 |
| 1997 | 1.20396 |
| 1996 | 1.16341 |
| 1995 | 1.19079 |
| 1994 | 1.2263 |
| 1993 | 1.31868 |
| 1992 | 1.38689 |
| 1991 | 1.33626 |
| 1990 | 1.12965 |
| 1989 | 0.944406 |
| 1988 | 0.907999 |
| 1987 | 0.893829 |
| 1986 | 0.924164 |
| 1985 | 0.886129 |
| 1984 | 0.865817 |
| 1983 | 0.914379 |
| 1982 | 0.953318 |
| 1981 | 0.981415 |
| 1980 | 0.95959 |
| 1979 | 1.10358 |
| 1978 | 1.05957 |
| 1977 | 1.00577 |
| 1976 | 0.95022 |
| 1975 | 0.985986 |
| 1974 | 0.91366 |
| 1973 | 0.954477 |
| 1972 | 1.07052 |
| 1971 | 1.26433 |
| 1970 | 1.165 |
| 1969 | 0.977243 |
| 1968 | 0.998461 |
| 1967 | 1.08888 |
| 1966 | 1.15489 |
| 1965 | 1.25017 |
| 1964 | 1.38905 |
| 1963 | 1.43916 |
| 1962 | 1.538 |
| 1961 | 1.65773 |
| 1960 | - |