| 年度 | 实际值 |
|---|---|
| 1995 | 7.6 |
| 1996 | 7.2 |
| 1997 | 6.35 |
| 1998 | 6 |
| 1999 | 5.7 |
| 2000 | 5.4 |
| 2001 | 5.13 |
| 2002 | 4.8 |
| 2003 | 4.1 |
| 2004 | 3.6649 |
| 2005 | 3.3 |
| 2006 | 3 |
| 2007 | 2.63237233268265 |
| 2008 | 2.4635761589404 |
| 2009 | 3.05371244418535 |
| 2010 | 2.77333281358113 |
| 2011 | 2.67316679467319 |
| 2012 | 2.56971743661452 |
| 2013 | 2.6 |
| 2014 | 2.4 |
| 2015 | 2.4 |
| 2016 | 2.4 |
| 2017 | |
| 2018 | 2.13 |