| 年度 | 实际值 |
|---|---|
| 1992 | 8.7 |
| 1993 | 8.6 |
| 1994 | |
| 1995 | 7.07 |
| 1996 | 9.28 |
| 1997 | 8.36 |
| 1998 | 4.3 |
| 1999 | 6.88 |
| 2000 | 8.03 |
| 2001 | 8.41 |
| 2002 | 6.65736067862128 |
| 2003 | 6.61 |
| 2004 | 6.5 |
| 2005 | 6.46 |
| 2006 | 5.51 |
| 2007 | 5.44762545096753 |
| 2008 | 5.02 |
| 2009 | 4.75 |
| 2010 | 4.46996290776358 |
| 2011 | 4.67 |
| 2012 | 6.95 |
| 2013 | 5.98 |
| 2014 | 4.65 |
| 2015 | 4.99 |
| 2016 | 3.23 |
| 2017 | 4.12 |
| 2018 | 2.53 |