| 年度 | 实际值 |
|---|---|
| 1995 | 31.3 |
| 1996 | 30.5 |
| 1997 | 30.53 |
| 1998 | 30.8 |
| 1999 | 39.6 |
| 2000 | 37.5 |
| 2001 | 35.87 |
| 2002 | 35.83 |
| 2003 | 31.01 |
| 2004 | 31.62 |
| 2005 | 26.6 |
| 2006 | 26.15 |
| 2007 | 23.48 |
| 2008 | 24.21 |
| 2009 | |
| 2010 | 23.56 |
| 2011 | 22.18 |
| 2012 | 21.65 |
| 2013 | 20.27 |
| 2014 | 19.64 |
| 2015 | 17.75 |
| 2016 | 18.34 |
| 2017 | |
| 2018 | 15.27 |