| 年度 | 实际值 |
|---|---|
| 1992 | 9.1 |
| 1993 | 7.6 |
| 1994 | |
| 1995 | 8.05 |
| 1996 | 8.65 |
| 1997 | 7.56 |
| 1998 | 3.56 |
| 1999 | 6.06 |
| 2000 | 10.2 |
| 2001 | 8.25 |
| 2002 | 9.28974300079116 |
| 2003 | 7.23 |
| 2004 | 7.54 |
| 2005 | 6.31 |
| 2006 | 6.29 |
| 2007 | 6.80546923555003 |
| 2008 | 6.08 |
| 2009 | 6.49 |
| 2010 | 7.13040559497961 |
| 2011 | 5.77 |
| 2012 | 7.11 |
| 2013 | 6.73 |
| 2014 | 6.71 |
| 2015 | 6.35 |
| 2016 | 11.58 |
| 2017 | 7.82 |
| 2018 | 8.56 |