| 年度 | 实际值 |
|---|---|
| 1995 | 30.4 |
| 1996 | 28.5 |
| 1997 | 28.38 |
| 1998 | 28.9 |
| 1999 | 28.4 |
| 2000 | 28.4 |
| 2001 | 27.77 |
| 2002 | 27.07 |
| 2003 | 26.4 |
| 2004 | 25.44 |
| 2005 | 24.36 |
| 2006 | 23.08 |
| 2007 | 19.36 |
| 2008 | 18.84 |
| 2009 | |
| 2010 | 18.4 |
| 2011 | 18.29 |
| 2012 | 17.77 |
| 2013 | 17.27 |
| 2014 | 15.5 |
| 2015 | 15.74 |
| 2016 | 16.53 |
| 2017 | |
| 2018 | 16.02 |